Endocrine effects of self-administration of high doses of anabolic steroids and testosterone were investigated in five power athletes during 26 wk of training, and for the following 12-16 wk after drug withdrawal. After 26 wk of anabolic steroid and testosterone administration, serum testosterone concentrations had increased 2.3-fold. This was associated with increased concentrations of serum estradiol, which rose 7-fold to values (0.48 nmol X 1(-1) typical for females. There was a major decrease in serum FSH and LH concentrations, but they returned to control levels following drug withdrawal. However, serum testosterone concentrations stayed at low levels (9 nmol X 1(-1) ) during this follow-up period, indicating long-lasting impairment of testicular endocrine function. Serum ACTH concentrations were also decreased during steroid administration, possibly due to a corticoid-like effect of some of the anabolic steroids taken in high doses. However, no changes were seen in serum cortisol. The only consistent change in the control group was an increase in serum LH concentrations during the most intensive training, suggesting that a decreasing tendency of serum testosterone was compensated for by augmented LH secretion.