The testes produce several hormones, but testosterone is by far the most important and abundant. Beyond testosterone, the testes also make inhibin B, anti-Müllerian hormone (AMH), and a small but meaningful amount of estrogen. Each of these plays a distinct role in male development, fertility, and overall health.
Testosterone: The Primary Testicular Hormone
Testosterone is the essential male sex hormone, and it’s produced by specialized cells called Leydig cells that sit in the spaces between the sperm-producing tubes of the testes. Like all steroid hormones, testosterone is built from cholesterol through a chain of chemical conversions. The process is triggered by luteinizing hormone (LH), a signal sent from the pituitary gland in the brain. When LH arrives at a Leydig cell, it kicks off a cascade that ultimately converts cholesterol into testosterone and releases it into the bloodstream.
Testosterone does far more than drive sexual function. It maintains muscle mass, bone density, red blood cell production, fat distribution, and mood. During puberty, it deepens the voice, triggers facial and body hair growth, and drives the development of the penis and testes themselves. In adult life, it remains critical for sperm production, sex drive, and energy levels.
Normal Testosterone Levels
In adult men, normal total testosterone typically falls between 300 and 1,000 ng/dL, depending on age and the lab doing the measurement. The American Urological Association considers levels below 300 ng/dL to be low in men without obesity, though some labs report values as low as 264 ng/dL as still within range. Testosterone peaks in early adulthood and gradually declines with age, roughly 1% per year after 30.
Because testosterone fluctuates throughout the day, peaking in the morning, accurate testing requires at least two blood draws between 7 and 10 AM on separate days. A single low reading isn’t enough for a diagnosis of testosterone deficiency.
What Low Testosterone Feels Like
When the testes aren’t producing enough testosterone, a condition called hypogonadism, the effects show up across the body. Common signs include a noticeable drop in sex drive, difficulty getting or maintaining erections, loss of spontaneous morning erections, reduced energy, and shrinking muscle mass. Some men develop breast tenderness or enlargement, increased irritability, difficulty concentrating, or depressed mood. When levels are very low, hot flashes can occur. Sperm counts also drop, which can lead to fertility problems.
These symptoms overlap with many other conditions, which is why the diagnosis requires both confirmed low blood levels and symptoms that match. Low numbers alone, or symptoms alone, aren’t sufficient.
Inhibin B: The Fertility Signal
The testes also produce inhibin B, a protein hormone made by Sertoli cells, the support cells that nurture developing sperm. Inhibin B acts as a feedback signal to the pituitary gland, telling it to dial back production of follicle-stimulating hormone (FSH). FSH is one of the key drivers of sperm production, so inhibin B essentially lets the brain know that sperm production is running smoothly and doesn’t need more stimulation.
This makes inhibin B a useful marker of testicular health, particularly the sperm-producing machinery. In adult men aged 8 to 30, normal levels range from about 47 to 383 pg/mL, with a gradual decline possible after 30. Low inhibin B levels can indicate problems with sperm production even before a semen analysis reveals an issue, making it a valuable early indicator of fertility status.
Anti-Müllerian Hormone in Development
During fetal development, the testes produce high levels of anti-Müllerian hormone. This hormone plays a one-time but irreversible role: it causes a set of embryonic tubes called Müllerian ducts to shrink and disappear. In the absence of AMH, those same ducts would develop into the uterus, fallopian tubes, and upper vagina. By eliminating them, AMH clears the way for male reproductive organs to form instead.
AMH levels remain high in boys through childhood and begin to decline at puberty as testosterone production ramps up. In clinical settings, AMH is sometimes measured in young boys to confirm that functional testicular tissue is present, for example, in cases where one or both testes haven’t descended into the scrotum. Normal AMH production in that scenario indicates the testes are healthy and working, just not in the expected position. Problems with AMH production during fetal life can lead to the development of internal female reproductive structures alongside male anatomy.
Estrogen From the Testes
It surprises many people, but the testes produce estrogen too. Specifically, they account for roughly 20% of the estrogen circulating in a man’s bloodstream. The remaining 80% is made in other tissues like fat, bone, brain, and skin, where an enzyme called aromatase converts testosterone into estrogen locally.
Within the testes, different cell types contribute to estrogen production at different life stages. In boys before puberty, Sertoli cells are the primary source. In adults, Leydig cells take over as the main producers because they express more aromatase. Developing sperm cells also contribute. This testicular estrogen isn’t just a byproduct. In men, estrogen helps regulate bone density, brain function, cholesterol metabolism, and even aspects of sperm maturation. Too little or too much can cause problems, which is one reason why hormone balance matters more than any single hormone’s level in isolation.
How These Hormones Work Together
The hormones produced by the testes don’t operate independently. They’re part of a tightly regulated feedback loop involving the brain. The hypothalamus releases a signaling hormone that tells the pituitary gland to produce LH and FSH. LH drives testosterone production in Leydig cells, while FSH supports sperm production in Sertoli cells. As testosterone and inhibin B levels rise, they signal back to the brain to reduce LH and FSH output. This loop keeps hormone levels within a functional range and ensures that sperm production matches the body’s signals.
When any part of this system breaks down, whether from aging, injury, genetic conditions, or medications, the effects ripple across multiple hormones. A man with damaged Leydig cells, for instance, won’t just have low testosterone. He’ll also have reduced estrogen production from the testes and elevated LH as the pituitary tries to compensate. Understanding the testes as a hormone-producing organ, not just a sperm factory, helps explain why testicular problems can affect energy, mood, bone strength, and body composition far beyond sexual function.