An analysis of the variations of semen quality in 45 men over a 9 month period was conducted. Semen quality parameters included semen volume, percentage of motile sperm, sperm count, sperm velocity, sperm morphology, and sperm viability. Semen analyses were done monthly during the same week of every month. Statistical variations were computerized using the Statistical Analysis System. Relationships investigated included between subject standard deviations, within subject standard deviation, intraclass correlations, total coefficient of variation, and the average individual coefficient of variation. Results showed that sperm count and semen volume had large intraclass correlations. Sperm velocity had low intraclass correlations. The additional parameters studied showed intraclass correlations in the intermediate range. Parameters resulting in large coefficients of variation included sperm count, percent motile sperm, and semen volume. The authors conclude that these statistical relationships can be used as indicators of precision of results obtained when a specific parameter is studied.