Seasonal variations of sperm characteristics.

A total of 1110 ejaculates were collected from 52 medical students over a 1-3-year period. Semen volume, sperm density, and total sperm count showed a maximum at the end of winter and beginning of spring and again in late fall. For the percentage of progressively motile and morphologically normal spermatozoa, a maximum is seen in late summer and a minimum in late winter/early spring. No bias seems responsible for these seasonal variations, which, if they are confirmed, should be taken into consideration when interpreting spermiograms.