Fourteen men each provided semen samples after 3, 6, and 10 days abstinence in a sequence decided by the individual and over a period of approximately 6 weeks. The proportion of sperm displaying progressive motility remained relatively constant up to 6 days but declined after a further 4 days of abstinence. This decrease was not associated with any major changes in sperm morphology or vitality. The total number of sperm with progressive movement in the ejaculate increased after 6 days and remained high after 10 days of abstinence. In subjects with asthenozoospermia, the greatest increase in the total number of sperm in the ejaculate occurred between 6 and 10 days. For men with reduced sperm quality participating in assisted fertilization programs, it may be advantageous to advise longer periods of abstinence, up to 10 days, prior to semen collection.