Mobiluncus is an anaerobic motile rod associated with bacterial vaginosis. In this work, luminol-enhanced chemiluminescence was used to study the ability of Mobiluncus spp. from the vaginas of women with bacterial vaginosis to induce, in the presence of normal adult serum, oxidative metabolism of polymorphonuclear leukocytes, which is an indirect measure of phagocytic activity. M. curtisii induced a significantly (p<0.05) lower response than M. mulieris, which indicates that M. curtisii escapes phagocytosis more easily. Indirect immunofluorescence assays showed IgG antibodies to M. curtisii at significantly (p<0.01) higher titres than to M. mulieris in women with bacterial vaginosis. The titres were higher in patients with bacterial vaginosis than in women without vaginosis and healthy men. No antibodies to Mobiluncus spp. of secretory IgA type were found in vaginal washings. These results indicate that M. curtisii is a more virulent species than M. mulieris, and agree with reports of M. curtisii found in postoperative and extragenital infections.