Plasma testosterone (T) and dihydrotestosterone (DHT) were measured in the plasma of otherwise healthy men ages 60-90 who had prostate hyperplasia. The androgens were measured by specific radioimmunoassays using paper and celite column chromatography. In the elderly subjects, plasma T was 466+/-35 (SE) ng per 100 ml which is reduced (p less than 0.05) as compared with values from younger men. In contrast, DHT levels were elevated when compared with values from men ages 20-39, 89 (53-152) versus 49 (33-74) 95% confidence ng per 100 ml. Analysis of data by the Mann Whitney U test demonstrates that the groups are different (p less than 0.001). These studies indicate that DHT levels and T/DHT ratios are altered in unstressed elderly men with BPH. Further study is necessary to delineate the source of DHT and whether these altered androgen levels are the cause of prostate hypertrophy or an unrelated effect of aging.