Variation of semen quality in normal men.

To examine the amount of variability in semen analysis results and whether there is any effect of season, 673 specimens provided by seven normal, healthy men (61-205 specimens/subject) over 72-324 weeks were assessed for sperm concentration, ejaculate volume, motility and motility index. Noticeable sample to sample variations were found. The largest proportion of the overall variance was due to within-subject differences, e.g., sperm concentration (54%), ejaculate volume (59%), percentage motility (96%) and motility index (74%). Although changes in semen-analysis results occurred over the year, no consistent trend was seen. No evidence was found to suggest that the differences were due to modifications of the methods employed by the laboratory, or to the change of season.