Male infertility may be due to a multiplicity of etiologic factors. In this study we have investigated the presence of cytomegalovirus (CMV) in 150 infertile men (selected after the exclusion of other etiopathogenic factors of infertility) and 80 subjects screened for pre-marriage consult. CMV was found in the sperm of 7/150 patients and 3/80 subjects screened for pre-marriage consult. Moreover, the seminal abnormalities evidenced in infertile men (a significant decrease of nemaspermic concentration and motility, of fructose, a significantly increased pH) were also observed in subjects screened for pre-marriage consult having CMV in the sperm. These abnormalities were related to alterations of cell-mediated immunity (decreased OKT4+, increased OKT8+ with decreased OKT4/OKT8 ratio). Among ten CMV+ subjects, two with idiopathic sterility and three subjects screened for pre-marriage consult showed a negativization of CMV in the sperm, during the observation period (one year), and a decreased anti-CMV titre lower than eight. Contemporary, a normalization of immunologic and seminal parameters was observed.