Men with testosterone levels in the highest quartile during the intervention period, as compared with all other subjects, were at elevated risk for cardiovascular-related events (hazard ratio, 2.4; P=0.05). Among subjects who were randomly assigned to the testosterone group, testosterone levels during the intervention period were available for 81 subjects. Cardiovascular-related events were reported in 4 of 14 subjects with testosterone levels higher than 1000 ng per deciliter during the treatment period, by 5 of 21 with levels of 500 to 1000 ng per deciliter, and by 7 of 46 subjects with levels of less than 500 ng per deciliter.