Twenty-eight strains of anaerobic curved rod-shaped (ACR) bacteria isolated from the female genital tract were examined and compared with reference strains of Bacteroides, Campylobacter and Wolinella and with 5 anaerobic strains associated with urethritis in male patients. The isolates were received from seven laboratories in Britain and Sweden during the past 12 months. The vaginitis isolates were divided into two groups according to the Gram staining reaction, cell morphology as studied by electron microscopy, biochemical activity tested by conventional and API ZYM tests, electrophoretic mobilities of cellular proteins and chemical compositions of chromosomal DNA. A number of important differences were revealed between the two groups, and between them and allied bacteria. The short Gram-positive (SCR), slightly curved rods had 1 to 3 subterminal lateral flagella and were biochemically more active than the long Gram-negative (LCR) strains, which were more curved and had 3 to 8 flagella. Both ACR groups were different from allied bacteria in their protein profiles and DNA base compositions: the Gram-positive strains had mol%G+C contents of 55.1 +/- 0.6, whereas those of the Gram-negative strains were 53.5 +/- 0.6 mol%. The protein profiles also indicated some heterogeneity within each of the ACR groups. We suggest these ACR strains comprise two distinct species, which are unrelated to the urethritis isolates with G+C contents of 29.9 +/- 0.9 mol% and to the reference strains.