The diagnosis of male adnexitis is difficult and the influence of this condition on fertility is still a matter of debate.With the intention to define diagnostic criteria a comprehensive study of biochemical and morphological features of semen, plus culture for microorganisms, was performed in patients who were assessed for infertility during a four year period.The following parameters were considered of diagnostic value:a) history of urogenital infection and/or abnormal rectal palpation.b) significant alterations in the expressed prostatic fluid and/or urinary sediment after prostatic massage.c) 1. Uniform growth of more than 103pathogenic bacteria, or more than 104non‐pathogenic bacteria per ml, in culture of diluted seminal plasma.c) 2. Presence of more than 106(peroxidase positive) leucocytes per ml of ejaculate.c) 3. Signs of disturbed secretory function of the prostate or seminal vesicles.The diagnosis of infection is accepted if either of the following combinations is found: a + b, a + c (1 or 2 or 3), b + c (1 or 2 or 3), c1 + c2, c1 + c3, c2 + c3.Many studies have been devoted to the question whether infection of the accessory sex glands can cause male subfertility; results are however discrepant and no final conclusion has yet been reached. Indeed, no controlled prospective study has been performed on subfertile men with infection, comparing the fertility outcome with or without treatment. This is, to a great extent, due to the confusion concerning the diagnosis of infection. Some authors diagnose infection as soon as pathogenic bacteria are cultured in the seminal plasma (Mobley 1975; Dahlberg 1976); some consider the number of bacteria per ml of ejaculate as an important diagnostic criterion (Clavequin et al. 1971; Drach 1975; Fari et al. 1977; Eneroth et al. 1978); others stress the diagnostic value of cytological examination of the expressed prostatic fluid (Eliasson 1968; Johannisson&Eliasson 1978); whereas some investigators consider certain changes in sperm morphology and in the biochemical composition of the seminal plasma of great importance (Anderson&Fair 1976; Blacklock&Beavis 1974; Eliasson i970; Lindholmer&Eliasson 1972).Since infection is defined on the basis of such different criteria, the reported incidence in subfertile men greatly varies from one series to another, and the results of treatment are very divergent (Marberger et al. 1972).The aim of this study is to report the results of our investigations on different parameters of infection of the accessory sex glands in male partners of childless couples, and to try to define diagnostic criteri