Significant among-donor differences in mean values for semen-specimen volume and sperm concentration, motility, forward progression, and morphology were demonstrated, but no correlation among these characteristics on a specimens-within-donor basis was demonstrable. When emission frequency was increased from 3·5 to 8·6 times per week, there was a decrease in specimen volume (—33%), in sperm concentration ( —55%) and motility ( —15%), but no effect on progression or morphology. At the high frequency, there was a decrease in total sperm number (—31%) and in motile sperm number (—41%) produced per week, but an increase in volume of semen per week (+39%). Specimens were rated at hourly intervals for 9 hr after collection; motility and progression declined at a linear rate with time, but no change in morphology was observed. No effect of seminal plasma on sperm motility or forward progression was noted in a complete factorial seminal-plasma-reversal study. No significant differences were observed in mean values for semen characteristics between masturbated and condom specimens.