Fifty-five strains received as Haemophilus vaginalis or as catalase-negative coryneform bacteria from the vagina together with 61 marker cultures were subjected to numerical phenetic analyses using 149 unit characters. The data were examined using the simple matching (SSM), Jaccard (SJ) and pattern (DP) coefficients and clustering was achieved using the average linkage algorithm. Cluster composition was not markedly affected by the coefficient used or by test error, estimated at 6 . 5%. The H. vaginalis strains formed a tight cluster which was only distantly related to representatives of the genera arthrobacter, Cellulomonas, Corynebacterium sensu stricto, Erysipelothrix, Haemophilus, Kurthia, Lactobacillus, Listeria and Propionibacterium but shared a high overall affinity to unclassified catalase-negative coryneforms which formed a discrete taxon, cluster 9. The H. vaginalis strains could be distinguished from the related strains in cluster 9 by several unrelated phenotypic characters. Using the S1 endonuclease assay, DNA-DNA hybridizations were performed with representative strains from the numerical as well as with reference strains of Bifidobacterium and Actinomyces. Haemophilus vaginalis was found to be a genotypically legitimate group and its DNA showed little homology with DNA from the marker strains tested. The DNA base composition of H. vaginalis was 42 to 44 mol % guanine plus cytosine. A new genus should be created to incorporate strains known as H. vaginalis or Corynebacterium vaginale. The name Gardnerella vaginalis proposed by Greenwood & Pickett (1979) is supported.