The contradictory findings concerning the influence of smoking on spermatogenesis that have so far been presented in literature were derived from fertility patients in retrospective studies; our data, in contrast, are based on a blind study of 333 voluntary test persons. The data of 95 smokers and 83 non-smokers remained to be evaluated after application of the following exclusive criteria: comparatively high consumption of alcohol, taking of drugs, taking of medicine, radioactive exposure, and genital diseases. Significant differences between the two groups were only found with regard to behavior; smokers revealed a higher rate of divorces, they drank alcohol and took drugs more frequently, and had had the first sexual intercourse at an earlier age than non-smokers. On the other hand, all spermatological parameters as well as the outcome of cytophotometric examination of the spermatozoon DNA showed a close correlation between smokers and non-smokers. Although an individual (toxic?) reaction to tobacco smoking cannot be ruled out, our findings lead to the conclusion that cigarette smoking has no detrimental influence on the spermatogenesis of healthy men between the age of 20 and 40.