In 65 adult diabetic men and 77 control men without diabetes, both groups without any problems as to fertility, the following characteristics of ejaculate have been compared: volume of seminal fluid, sperm concentration per milliliter, total sperm count, sperm morphology, and motility at 1, 3, and 5 hours after ejaculation. In the entire diabetic group, sperm morphology and motility at 1 hour after ejaculation was statistically significantly worse. In 15 diabetics without sexual disurbances only sperm morphology was statistically significantly worse compared with an equally large control groups. In 50 diabetics with erection disturbances, sperm volume and motility in three successive observations were statistically remarkably lower. In younger age subgroups, the differences between diabetics and nondiabetics were more marked than in older age subgroups. The patients' age, when diabetes was discovered in them, did not essentially influence the quality of the ejaculate where diabetes lasted 8 or more years. Diabetics over 40 years' age displayed a significantly lower sperm volume. The total sperm count and motility at 3 and 5 hours after ejaculation, with 12 or more years' duration of diabetes, differed from diabetes of 2 years' duration. On the basis of these observations a negative influence of diabetes on the quality of the ejaculate seems unquestionable. There exists great variability in the adverse effect on the individual diabetic. Also, the individual characteristics of the ejaculate are affected, usually, to a different extent: the most frequently and markedly affected being the sperm motility, then morphology and/or volume of ejaculate, and the least often and the least conspicuously, the sperm count.