In young men, chronic ingestion of 100 mg androstenedione (ASD), three times per day, does not increase serum total testosterone but does increase serum estrogen and ASD concentrations. We investigated the effects of ASD ingestion in healthy 30- to 56-yr-old men. In a double-blind, randomly assigned manner, subjects consumed 100 mg ASD three times daily (n = 28), or placebo (n = 27) for 28 days. Serum ASD, dihydrotestosterone (DHT), free and total testosterone, estradiol, prostate-specific antigen (PSA), and lipid concentrations were measured at week 0 and each week throughout the supplementation period. Serum total testosterone and PSA concentrations did not change with supplementation. Elevated serum concentrations of ASD (300%), free testosterone (45%), DHT (83%), and estradiol (68%) were observed during weeks 1-4 in ASD (P < 0.05). There was no relationship between age and changes in serum ASD (r2 = 0.024), free testosterone (r2 = 0.00), or estradiol (r2 = 0.029) concentrations with ASD, whereas the serum DHT response to ASD ingestion was related to age (r2 = 0.244; P < 0.05). Serum concentrations of high-density lipoprotein cholesterol were decreased by 10% during the supplementation period (P < 0.05). These results suggest that the ingestion of 100 mg ASD, three times per day, does not increase serum total testosterone or PSA concentrations but does elicit increases in ASD, free testosterone, estradiol, and DHT and decreases serum high-density lipoprotein cholesterol concentrations.