Correlations between sex hormone levels and the male depth of voice were investigated in 102 singers. As compared to tenor singers higher testosterone and lower oestradiol plasma concentrations were measured in bass and baritone singers. This resulted in higher testosterone/oestradiol ratios due to increased androgens in those with deeper voices. Deeper voices were associated with taller and heavier body build. In the young age group sexual activity was highest among the bass voices, in the middle and old age group tenors were most active. There were no depth of voice-related differences as regards the sequence and occurrence of different pubertal characteristics. Only future bass singers had an increased of acne. The results indicate that the different depths of the male voice are influenced by different concentrations of circulating sex hormones and also by the androgen sensitivity of the target organs.