This paper examines the issue of whether workers learn productive skills from their co-workers, even if those skills are unethical. Specifically, we estimate whether Jose Canseco, a star baseball player in the late 1980’s and 1990’s, affected the performance of his teammates by introducing them to steroids. Using panel data, we show that a player’s performance increases significantly after they played with Jose Canseco. After checking 30 comparable players from the same era, we find that no other baseball player produced a similar effect. Furthermore, the positive effect of Canseco disappears after 2003, the year that drug testing was implemented. These results suggest that workers not only learn productive skills from their co-workers, but sometimes those skills may derive from unethical practices. These findings may be relevant to many workplaces where competitive pressures create incentives to adopt unethical means to boost productivity and profits. Our analysis leads to several potential policy implications designed to reduce the spread of unethical behavior among workers.