Semen samples of 190 men attending an andrology clinic were evaluated with bacteriological culture and categorized as negative (group I) and positive (group II); the effect of bacteriospemia on semen characteristics was also analyzed. Semen samples from both groups were simultaneously analyzed for routine parameters such as volume, sperm count, motility, viability and morphology. The semen culture was negative in 34% and positive in 66% of the samples. From 123 samples, 157 aerobes and 8 anaerobes were recovered. The most commonly isolated organism was Staphylococchs epidermidis (in 63% of the samples), followed by Streptococchs viridans (28%), Escherichia coli (9%), Staphylococcus aureus (5%), Streptococcus faecalis (5%), beta-hemolytic Streptococcus (4%), and Enterobacter agglomerans (4%). Other microorganisms, including Klebsiella sp, Candida sp., and Proteus mirabilis, were recovered in fewer than 4% of the specimens. The comparison of semen characteristics between infected and noninfected men showed that motile spermatozoa and viability were lower when the microorganisms were present in the semen. It would appear that the bacteria can have a direct effect on semen quality with negative consequences in fertility.