For women at risk to develop schizophrenia, estradiol has been postulated to constitute a protective factor. Women suffering from psychotic disorders have accordingly been found to exhibit lower estradiol levels than controls. Our aim was to study gonadal function in psychotic men to determine the gender specificity of these observations, as available data in men are more scarce and conflicting and largely disregarded estradiol. Serum hormone levels were examined in 34 men admitted consecutively for an acute exacerbation or first onset of schizophrenia in a blinded prospective design. Subjects with current affective disorder including manic episode, concomitant substance abuse or severe medical illness were excluded. A control group of 34 healthy male blood donors was recruited. As compared to matched controls, acutely admitted men suffering from schizophrenia exhibited significantly lower serum levels of estradiol, oestrone, testosterone and free testosterone. Although results have to be regarded as preliminary, acute exacerbation of schizophrenia in men seems to be associated with low serum oestrogen and androgen levels. The oestrogen hypothesis postulating a protective action of estradiol concerning schizophrenia for women might well be valid for both genders. However, future research is needed before clinical applications are justified.