The accuracy of two new 4-h identification systems for anaerobes, the AN-IDENT (Analytab Products, Plainview, N.Y.) and the RapID ANA (Innovative Diagnostic Systems, Inc., Atlanta, Ga.) was compared with that of the API 20A system (Analytab Products). A total of 132 clinical isolates were tested in each of the three systems. The overall accuracies at the genus and species level for the three systems were: API 20A, 68.9 and 56.8%, respectively; AN-IDENT, 90.2 and 73.5%; and RapID ANA, 93.9 and 81.8%. Improved identification of anaerobes with the AN-IDENT and the RapID ANA systems was observed for isolates of the genus Fusobacterium, Clostridium species other than Clostridium perfringens, non-spore-forming bacilli, and isolates of the genus Peptostreptococcus. Reproducibility studies demonstrated that the results of the individual test reactions in all three identification systems were reproducible when the interpretive guidelines of the manufacturer were followed precisely.