No significant differences were found between mean values calculated for daily increases in abstinence for any semen analysis parameter, with the exception of ejaculate volume between 1 and 2 days of abstinence. However, graphical analysis revealed significant trend lines for both ejaculate volume and total sperm count. The mean ejaculate volume increased by 1.0 ml between the first and second days of abstinence, and at approximately 0.3 ml/day thereafter until the 5th day. The total sperm count showed a mean daily increase of 50-60 x 10(6) spermatozoa/day. Quantitative differences exist in the evolution of these two parameters in comparison to normal fertile men. There were decreased mean percentages of motile and viable spermatozoa at short periods (less than or equal to 1 day) of abstinence, increasing up until the 2nd (% viable) or 3rd (% motile) days of abstinence, with decreased values at greater than 5 days. The mean percentage of morphologically normal spermatozoa was unaffected by the duration of abstinence. Delays of up to 3 hr between ejaculation and analysis did not seriously affect the mean semen parameters.