Illustration of a man deriving strength and power from a monkey’s testicles, while the sad-looking monkey eats a banana.
Illustration: Juta

The Strange History of Men Going Nuts for Monkey Testicle Transplants

Invented by surgeon Serge Voronoff, the operation was once seen as an elixir of eternal youth and sexual prowess.

This article originally appeared on VICE Italy.

Science has come a long way since the 1920s.

Back then, doctors had very limited knowledge of how transplants worked, meaning some believed that a testicle transplant could help people experiencing impotence. Since it was hard to find anyone willing to part ways with a healthy organ, scientists started looking into cross-species transplantation. In theory, it offered the prospect of an enormous supply of donor material, resolving the problem of the shortage of human tissue.


Of course, nowadays this sounds ludicrous, not least because we know that impotence can be caused by a variety of issues, some physical and some psychological, and that in many cases it has nothing to do with the functioning of the testicles.

One of the pioneers of testicle transplantation research at the time was surgeon Serge Abrahamovitch Voronoff. Born in Russia in 1866, Voronoff moved to France for his studies, later becoming a French citizen. Between 1896 and 1910, Voronoff worked in a clinic in Egypt, where he became interested in the long-term effects of castration, which was believed to prolong a man’s life (a correlation also found by some recent studies of centuries-old data).

Voronoff devoted his entire career to exploring the link between gonads and the longevity of life. He was convinced that the secret to eternal youth lay hidden in our sex hormones, and he wasn’t alone: in 1889, Charles-Édouard Brown-Sequard, one of the fathers of modern endocrinology (the science of hormones), injected himself with an extract of finely ground dog and guinea pig testicles. Inspired by the experiment, Voronoff tried the bizarre life-extending elixir on himself. The serum did not have the desired effect. 

Despite this setback, Voronoff grew even more confident in his ideas after his time in Egypt. Over the following ten years, he performed testicle transplants on more than 500 goats, sheep and bulls, implanting organs from younger specimens into older ones. He observed that the new set of jewels had reinvigorating effects on older animals, and was convinced he had discovered a method for slowing down the ageing process.


The surgeon then moved on to experimenting on humans, transplanting monkey thyroid glands onto patients with hypothyroidism (an underactive thyroid gland). For a short while, he even experimented with grafting testicles of recently-executed prisoners onto his patients, but this proved too logistically difficult to keep up with demand. So Voronoff turned to primates.

Naturally, his patients weren’t enthusiastic about swapping their testicles with those of a monkey, so Voronoff developed a treatment where he’d insert thin slices of baboons’ and chimpanzees’ testicles into the scrotum of men. The graft, only a few millimetres in size, would quickly merge with the human tissue. He promised his treatment had miraculous benefits: increased memory, reduced fatigue, enhanced eyesight and libido – plus, of course, a longer and more youthful life. The operation, Voronoff boldly suggested, might even help to cure schizophrenia. 

The first official transplant of a monkey gland on a human body took place on the 12th of June, 1920. Three years later, Voronoff’s work was applauded by over 700 scientists at the International Congress of Surgeons in London.

Voronoff’s treatment became hugely popular. Millionaires across the world signed up for the surgery, and by the early 1930s thousands of people had been under the knife, including 500 in France alone. To cope with the dizzying increase in demand, Voronoff opened a monkey farm in a villa on the Italian riviera, near the French border. Voronoff’s Castle, as it came to be known, was entrusted to a former circus animal keeper and equipped with a laboratory to collect tissue. 


Women of the time soon demanded their own version of the treatment for prolonged youth, prompting Voronoff to develop a monkey ovary transplant. The surgeon also implanted a human ovary into a monkey and then tried to inseminate it with human sperm. Unsurprisingly, the second half of this experiment didn’t work. 

Voronoff’s success afforded him a lavish life – he occupied a whole floor of one of Paris’ most expensive hotels with his entourage of butlers, valets, secretaries, drivers, two chiefs of staff and a few rumoured mistresses. But the surgeon’s career came to an abrupt end when it became clear that his transplants didn’t bring about the benefits he had advertised; experts ascribed initial improvements to the placebo effect.  

Meanwhile, in the Netherlands, the now-defunct pharmaceutical company Organon isolated testosterone for the first time in 1935. Voronoff welcomed the news, as it confirmed his theories about the existence of a substance made by the sexual glands. To his great disappointment, however, experiments with testosterone injections didn’t rejuvenate and strengthen the human body. 

By the 1940s, Voronoff’s treatments were essentially branded as bogus. When he died in 1951 after a fall, few newspapers reported his death, and those that did ridiculed him. In the 1990s, some scientists even blamed Voronoff’s experiments for the mutation that allowed the HIV virus to infect humans, but that claim was later debunked.

Today, the surgeon’s intuitions about mammals’ sexual glands are regarded as important contributions to modern endocrinology, biology and hormone replacement therapy. His monkey transplants, however, join the ranks of medical oddities the scientific community would rather forget.