A commercially available fluorescein-conjugated monoclonal antibody (MAb) (Syva Co., Palo Alto, Calif.; Genetic Systems, Seattle, Wash.) against Neisseria gonorrhoeae was compared with a standard cystine Trypticase agar (CTA) sugar utilization method and with three rapid carbohydrate utilization tests, including the Minitek (BBL Microbiology Systems, Cockeysville, Md.), Neisseria-Stat (Richardson Scientific, Dallas, Tex.), and Neisseria-Kwik (Micro-Biologics, St. Cloud, Minn.) systems for the identification of Neisseria species. The MAb correctly identified all 86 clinical isolates of N. gonorrhoeae. Of these 86 isolates, 28 were found later (48 h after the initial inoculation) to be contaminated with non-Neisseria bacteria. In the other four test systems studied, the identification rates for pure and contaminated N. gonorrhoeae cultures were, respectively, as follows: CTA sugars, 88 and 32%; Minitek, 67 and 50%; Neisseria-Stat, 97 and 96%; and Neisseria-Kwik, 80 and 74%. The MAb did not identify any of the 50 nongonoccocal Neisseria isolates tested. The most expensive test system was the MAb, followed by the Neisseria-Kwik, Minitek, Neisseria-Stat, and CTA sugars systems. The MAb appears to be a rapid and accurate method to identify in vitro isolates of N. gonorrhoeae.