The data from previous studies on the seminal concentrations of proteic hormones result in the hypothesis that there exists a selective filter for these hormones, which is between the systemic circulation and the male genital canal. Previous data regarding sexual steroids are insufficient to verify if such a filter system also operates in the case of hormones of minor molecular weight. It would appear that the study of cortisol, a non-sexual steroid, will be more useful. The concentrations of this hormone in the peripheric blood (176 +/- 59, mean +/- ds, ng/ml) prove to be much greater than in the seminal plasma (20 +/- 9.6). No significant differences are found between normozoospermic and oligo-azoospermic subjects, either in the blood (173 +/- 184 +/- 53), or in the seminal plasma (21 +/- 12 versus 20 +/- 8). These data would seem to support the hypothesis under discussion.