To assess the existence of a possible immunologic factor in varicocele-associated infertility, we searched for antispermatozoal antibodies in serum, seminal plasma, and bound to spermatozoa in 32 infertile men with varicocele and 22 infertile patients without palpable varicocele, with the use of an enzyme-linked immunosorbent assay. In addition, we performed morphologic and microbiologic analyses of the semen and urethral smears for isolation of Chlamydia trachomatis. Twenty-nine men from the varicocele group (90.6%) demonstrated antispermatozoal antibodies, compared with only 9 men (40.9%) in the control group. The antibodies in both groups, when present, were mainly serum and seminal plasma immunoglobulins IgA and IgM. A significant quantitiative difference between the varicocele and control groups was also observed for serum IgA, seminal plasma IgA and IgM, and sperm-bound IgG, IgA, and IgM. Oligozoospermia and asthenozoospermia were significantly more prevalent in the varicocele men. An asymptomatic genital tract infection with C. trachomatis, Ureaplasma urealyticum, and Escherichia coli was traced in 40.6% of the varicocele men and in 45.5% of the control group. No interaction could be demonstrated between the infection and antispermatozoal antibody formation. These data suggest that an immunologic factor may play a role in varicocele-associated infertility; however, its impact on reproduction has yet to be assessed.