Sperm-mucus interaction under in-vitro or in-vivo conditions might be affected by microorganisms colonizing the reproductive tract. In order to study the influence of antimicrobial therapy, an extensive microbial screening was performed including Chlamydia trachomatis, Mycoplasma hominis, Ureaplasma urealyticum, Neisseria gonorrhoeae, a broad spectrum of potentially pathogenic aerobic and anaerobic bacteria, Trichomonas vaginalis, herpes simplex virus and yeasts. One-hundred-and-six couples with a mean duration of infertility of 5.5 years (range 1-12 years) and with isolation of potentially pathogenic microorganisms in semen samples and/or cervical swabs were submitted to a prospective pilot study. None of the patients displayed signs or symptoms of infection in the lower genital tract. Before and after specific therapy, based on antimicrobial susceptibility testing, sperm analyses and in-vitro sperm penetration meter tests (SPMT) (Kremer) were performed. SPMT was evaluated with cervical mucus of patients' wives, collected after a standardized oral treatment with oestrogens and, additionally, in a crossed manner with cervical mucus and spermatozoa of fertile donors. The success of antimicrobial therapy was controlled by repeating the same microbial screening and was 96%. However, there was a marked change in the microbial pattern. A comparison of the results of sperm analyses before and after treatment revealed neither significant differences for sperm volume, sperm count, propulsive motility, morphology, vitality, pH, fructose concentration or number of round cells, nor was there a significant influence on the cervical index and the number of leukocytes in cervical mucus.(ABSTRACT TRUNCATED AT 250 WORDS)