The semen characteristics studied were the sperm count, semen volume, morphology and pre-freeze and post-thaw motility. Two categories of fertile men were investigated: semen donor candidates for artificial insemination and pre-vasectomy subjects. Since mean values for each variable in the two series were similar, they could be considered as a single group of 484 fertile men. Only those subjects whose ejaculates were obtained after an abstinence of 5 days or less were retained. The distribution, mean and percentiles were determined for each variable. The 10th and 90th percentiles for sperm count, percentage of motile forms and percentage of normal cells were respectively 25 and 180 million per ml, 60% and 80% and 50% ad 75%. The three variables, sperm count, semen volume and total number of spermatozoa which were dependent on abstinence were analysed in the same manner for 3 days of abstinence. The group studied seemed to be as representative and as well defined as possible.