In this study, we investigated the seminal inflammatory response to egg infestation of the urogenital organs in 240 semen-donating men aged 15-49 years living in a Schistosoma haematobium-endemic area of Madagascar. In 29 subjects (12%) with excretion of > or =5 ova/ejaculate, leukocytospermia (>10(6) leukocytes/mL) and the presence of seminal lymphocytes and eosinophil leukocytes were each significantly more prevalent than in 74 subjects (31%) who were S. haematobium negative (P<.01). In addition, seminal levels of interleukin (IL)-4, IL-6, IL-10, and tumor necrosis factor- alpha were significantly higher among seminal egg-excreting subjects than among infection-negative subjects (P<.001). Sexually transmitted infection (STI) with Neisseria gonorrhoeae, Chlamydia trachomatis, Mycoplasma genitalium, and/or Trichomonas vaginalis did not act as a confounding factor for the observed associations. At follow-up, 6 months after systematic antischistosomiasis and STI syndrome treatment at baseline, the prevalence of seminal leukocytes decreased significantly among the previously seminal egg-positive subjects. The same tendency was observed for the posttreatment levels of cytokines. Numerous studies have already shown an association between STI-associated genital inflammation and human immunodeficiency virus (HIV) propagation. Therefore, the results of the present study suggest that male urogenital schistosomiasis may constitute a risk factor for HIV transmission, as a result of egg-induced inflammation in the semen-producing pelvic organs.