The mean semen parameters and their interrelationships are reported for the first semen analyses performed on a population of 1801 suspected infertile men. For this population, the mean (+/- SD) sperm density was 84.3 (+/- 78.3) x 10(6)/ml, the mean volume was 3.3 (+/- 1.7) ml, and the mean total sperm count was 265.6 (+/- 270.0) x 10(6)/ejaculate. After exclusion of 90 cases of azoospermia (5.0% of the patients), these values became 88.7 (+/- 77.8), 3.4 (+/- 1.7), and 279.5 (+/- 269.9), respectively. For the population of patients with spermatozoa in their semen, the mean (+/- SD;n) percentages of motile, viable and morphological normal spermatozoa were 50.3 (+/- 15.4; 1677), 77.3 (+/- 11.9; 830), and 54.2 (+/- 11.7; 1587), respectively. Loge transformation of the sperm density values in sperm-positive ejaculates gave a mean of 51.9 x 10(6)/ml with 95% confidence limits of 12.3 to 219.0 x 10(6)/ml. Ejaculate volume was slightly, but significantly, reduced in cases of azoospermia and polyzoospermia (i.e., greater than 200 x 10(6)/ml). Significant positive correlations were found between sperm density and the parameters of sperm quality, and also between these latter three parameters themselves. Increasing semen viscosity had no effect upon the morphology of the spermatozoa, but in ejaculates with marked or high viscosity the motility and viability of the spermatozoa were significantly depressed.