Comma-shaped rods isolated from the vagina of women with signs of vaginitis were studied. Three types of rods were found: a long (length about 4 microns), a medium-sized (about 3 microns) and a short (about 1 micron) variant. All three variants had a characteristic cork-screw motility. The long and the medium-sized variants had up to eight flagella, while the short had up to four. The bacteria only grew under anaerobic conditions, although after a great number of passages on artificial culture media the short variant, but not the other variants, could be grown in a microaerophilic atmosphere. In broth media growth of all three variants was stimulated by the addition of 0.3% formatefumarate. On solid media colonies developed after incubation for 48 to 72 hours at 37 degrees C. The long and the medium-sized variants differed from the short variant in that they produced leucine arylamidase, while only the short variant produced alpha-galactosidase. None of the strains utilized carbohydrates; intravariant differences were found in the test results for gelatin and nitrate reduction. All strains of the short variant tested, but none of the long, hydrolysed sodium hippurate. Gas chromatographic analyses showed that all three variants produce acetic, lactic and succinic acids.