Bacterial culture of semen samples from 100 male partners in infertile couples revealed the presence of aerobic bacteria in 49 cases. Streptococcus faecalis ( Enterococcus) was isolated from 53%, micrococci species from 20% and α-haemolytic streptococci from 16% of the infected samples. The incidence of oligozoospermia and teratozoospermia was significantly ( P < 0.05) higher in men whose semen samples contained S. faecalis than those whose semen samples contained micrococci or α-haemolytic streptococci or those that did not contain bacteria. The mean sperm concentration, as well as the mean percentage of morphologically normal spermatozoa, was significantly ( P < 0.03) lower in semen infected with S. faecalis compared with that containing micrococci or α-haemolytic streptococci and the uninfected samples. There is a high incidence of semen infection with S. faecalis, and it is associated with compromised semen quality in terms of sperm concentration and morphology. The presence of micrococci or α-haemolytic streptococci does not appear to have any detrimental effect on sperm quality.