Summary:A screening of 3196 semen analyses performed in our clinic from January 1986 to December 1990 revealed 314 (9.8%) patients whose semen was infected withBacteroides ureolyticus. Investigating the relationship between the presence ofB. ureolyticus, the seminal microflora and the conventional semen parameters, we observed that the presence of this micro‐organism in the semen was coupled (1) to an increased presence ofEnterococcusspecies, (2) to an increased number of short‐tailed spermatozoa and epithelial cells, and (3) to a decreased total fructose concentration (mg ejaculate−1). These results suggest thatB. ureolyticusor its toxins may influence sperm morphology and function by yet unknown mechanisms and may also increase the number of epithelial cells by soft tissue infectionin vivo. The decreased fructose levels suggest that this anaerobic micro‐organism might specifically colonize the seminal vesicles, while the normal zinc values recorded suggest a normal prostatic function. Overall, our data support the hypothesis that the presence ofB. ureolyticusis not associated with nongonococcal ure