Published November 12, 2026 by PETA Staff.

First, there was the blood.

University of Minnesota laboratory staff found blood in the cage of a monkey named Chico, the first sign that something was wrong.

Then there was a wound.

These photos, obtained by PETA through a public records request, show stitches in a deep wound Chico inflicted on himself when bleak and lonely conditions at the University of Minnesota drove him into a state of mental distress so severe that he self-mutilated.

Staff discovered a deep wound on Chico’s scrotum. It was stitched closed and nearly healed. Three weeks later, he tore into himself again, this time leaving a wound about five inches long and exposing his testicle. In records PETA obtained, staff wrote: “It looked like he grabbed his whole left scrotum and bit down on it.”

Infection followed.

Chico’s testicle became swollen, hot, hard, and red. Surgery removed his left testicle and damaged scrotal tissue. Records described the testicle as decaying, bruised, and mangled.

But Chico didn’t stop mutilating himself.

The stressed macaque continued harming himself for months. He injured his forearm, shoulder, and legs. He paced in his cage. He pulled out his hair. He bit himself on his thigh so deeply that the nickel-sized wound extended into muscle. It was so severe that it had to be surgically closed in layers.

Staff found large purple bruises, additional puncture wounds on his scrotum, and dried blood on his shoulder.

“I don’t know what’s stressing him”

Staff were perplexed. One veterinarian wrote: “I don’t know what’s stressing him so much.” Staff gave him a box that used to hold latex gloves filled with shredded paper, in an apparent DIY attempt to give Chico an activity to occupy his mind. When that didn’t work, they gave him another box, adding cereal, then treats, to the shredded paper.  

Chico bit his scrotum again, leaving puncture marks requiring stitches.

Despite the name, a laboratory “play cage” like the one Chico was placed in consists merely of four connected metal cages, allowing movement only from one barred enclosure to another. Photo for illustrative purposes only.

Records indicate that Chico was likely housed alone—a particularly distressing environment for a highly social primate—in a cage barely bigger than his body. At one point, he was moved to a “play cage”—a pathetic attempt to give him more room—when he was not being experimented on. He continued pulling out his hair. He was moved to an all-male unit after staff suggested that the proximity of female monkeys may be the problem. Chico still paced and bit his shoulder. One veterinarian said, “I’m willing to try anything.”

Anything except sending him to a sanctuary.

Experiments Continued

During most of this time, experimenters continued to administer experimental drugs into Chico despite his near-constant injuries. Records PETA obtained do not indicate what the experiment was or what procedures Chico endured. What we do know is that experiments on Chico continued despite clear and repeated evidence that he suffered from extreme stress.

Four months after staff first discovered blood in his cage, Chico finally got a break. Staff replaced his regular experimental drug with a daily antidepressant. It worked for a while, records show. But three weeks later, staff reported that Chico resumed biting his scrotum and arm.

It is not known if Chico was ever removed from experimentation.

Days later, the last record entry says that Chico was not biting himself. They do not say what eventually became of him.

A Tradition of Suffering

Chico’s story is not new. Records place these events in 2012, but the plight of monkeys in University of Minnesota laboratories did not end with him. More than a decade later, monkeys continue to suffer in experiments conducted by Jan Zimmermann and Matt Johnson.

The two conduct curiosity-driven experiments, subjecting monkeys to craniotomy surgeries. They slice open a monkey’s scalp, remove part of the skull, affix headposts and cranial recording chambers, and implant electrodes and other hardware directly into the brain. Neither experimenter is a surgeon.

Zimmermann drilled 20 screws so deep into the skull of a monkey named Everett that they pierced his brain. Everett suffered for weeks while Zimmermann tried to hide his incompetence.

Johnson’s record is similarly disturbing. One implant sheared off the skull of a monkey named Ponyo, who suffered for weeks from an infection while blood leaked from one of her screw holes.

What You Can Do

The university suspended Geoff Ghose after PETA exposed the experimenter’s incompetence and met with local law enforcement officials, presenting evidence of apparent animal welfare violations in his laboratory. Please take action below to demand that the school permanently bar Jan Zimmermann and Matt Johnson from experimenting on monkeys.