Bacteria-free filtrates of nine strains of Bacteroides ureolyticus, most of which had been isolated from the urethra of men with non-gonococcal urethritis, damaged the mucosal epithelium of human fallopian tube and bovine oviduct organ cultures. The damage, pronounced after three days, was manifested by loss of ciliary activity. Histological observations, supported by scanning electron microscopy, showed that this loss was due to disruption of the epithelia with sloughing of cells. It is likely that the inhibitory activity of the filtrates was due to endotoxin since lipopolysaccharides extracted from the bacteria had a similar deleterious effect on oviduct mucosal epithelia. It is speculated that B. ureolyticus has the potential for causing damage to the urethral mucosa by the same mechanism.