The chromosomal constitution of 1582 human sperm from 30 normal men of proven fertility was investigated after sperm penetration of hamster eggs. A minimum of 30 sperm chromosome complements were analysed per donor so that the distribution and variation in the frequency and type of sperm chromosomal abnormalities could be assessed. The mean frequency of sperm chromosomal abnormalities in individual men was 10.4% (+/- 6.0%) with a range of 0-24.7%. For numerical abnormalities the mean was 4.7% (+/- 2.9%) with a range of 0-10% and for structural abnormalities the mean was 6.2% (+/- 6.0%) with a range of 0-23.1%. The 95% confidence intervals for the mean of an individual male were 0-10.5% for numerical abnormalities, 0-18.2% for structural abnormalities, and 0-22.4% for total abnormalities. There was a significant excess of hypohaploid complements compared with hyperhaploid complements. Since hypohaploid complements could be caused by technical artefact, a conservative estimate of aneuploidy was obtained by doubling the frequency of hyperhaploid sperm, yielding an estimate of 2.4% aneuploidy. The proportion of X-bearing (53%) and Y-bearing (47%) sperm did not differ significantly. These results were compared to the other two large studies of sperm chromosome complements from normal men.