The RapID ANA system (Innovative Diagnostic Systems Inc., Atlanta, Ga, USA), a 4-hour micromethod for identifying clinically important anaerobic bacteria, was evaluated using 196 anaerobic clinical isolates and the results were compared with those obtained by applying conventional Virginia Polytechnic Institute (VPI) methodology. The identifications achieved by the RapID ANA system for 141 (72%) of these isolates agreed with the species identifications obtained using VPI methodology, without the need for additional tests. A further 40 (20%) were in agreement after performance of additional suggested tests, 11 (6%) were misidentified and 4 (2%) could not be identified using the RapID ANA system. Excellent agreement between the two methods was demonstrated for the Gram-positive cocci and good agreement for the Gram-negative bacilli. The RapID ANA system was suboptimal in the identification of Clostridium species other than C. perfringens.