A prominent California medical school has apologized for conducting dozens of unethical medical experiments on at least 2,600 incarcerated men in the 1960s and 1970s, including putting pesticides and herbicides on the men’s skin and injecting it into their veins.

Two dermatologists at the University of California, San Francisco — one of whom remains at the university — conducted the experiments on men at the California Medical Facility, a prison hospital in Vacaville that’s about 50 miles northeast of San Francisco. The practice was halted in 1977.