Serum prolactin levels and sexual function were evaluated in 28 men from 60 to 64 years of age and in 44 men from 65 to 70 years of age. All subjects were married, physically healthy, and had no psychopathology or marital problem. About a third of the men aged 60 to 70 years suffered from impotence. No obvious correlation between elevated levels of serum prolactin and impotence was obtained. Subjects aged 65 to 70 who had decreased libido exhibited a significant elevation of serum prolactin levels, while subjects of the same age group who had reserved (normal) libido appeared to have low serum prolactin levels. Nine of ten men aged 60 to 70 years with serum prolactin levels above 40 ng/ml reported decreased libido. Potent men of both age groups (60-70 years) with high prolactin levels showed a tendency to have a decrease in frequency of sexual intercourse. Thus, it seems that mild hyperprolactinemia in aging men may be associated with decreased sexual desire and frequency of sexual activity.