Diamine oxidase (DAO), an enzyme which degrades polyamines, is present at a very high level in human seminal plasma and is assumed to come mainly from the prostate. The possible relationships between DAO activity and biochemical markers of accessory sex glands were evaluated in 139 men in barren marriages. Four groups were formed: normozoospermic (n = 41), asthenozoospermic (n = 29), oligoasthenozoospermic (n = 35) and azoospermic (n = 34). DAO activity was the highest in the asthenozoospermic group and was significantly different from that in the azoospermic one. For all specimens, a positive correlation was demonstrated between DAO activity and the prostatic markers citric acid and acid phosphatase. However, DAO activity was correlated with citric acid only in the oligoasthenozoospermic and the azoospermic groups. Acid phosphatase and citric acid were linked in all groups. These results implicate the DAO enzyme in changes in sperm metabolism leading to a loss of motility and suggest that DAO comes partly from the upper part of the genital tract (testis and/or epididymis), in addition to the prostatic gland secretion, accounting for the absence of correlation with prostatic markers in normozoospermic and asthenozoospermic groups.