OBJECTIVE:The dihydrotestosterone:testosterone ratio seems to be an important factor in the expression of androgenic activity, especially in the prostate and pilosebaceous unit. Whereas the decline of testosterone (T) in aging men is well known, controversial data can be found in literature concerning the age dependence of dihydrotestosterone (DHT) levels. Data from the database of the Institute of Endocrinology served as the basis for the definition of the life span curve for the ratio dihydrotestosterone : testosterone. METHODS:The results of testosterone and dihydrotestosterone obtained immunoassays from 10 251 male patients were used in the construction of the curve. RESULTS:The data show that after a peak of DHT:T in infancy and a subsequent decrease in puberty, the ratio of both androgens remains practically without change from approx. 20 years of age till old age. CONCLUSION:High DHT:T ratio in infancy decreases at puberty and throughout the entire reproductive period of life this ration remains practically constant.