The Superoxol (Merck & Co., Inc., Rahway, N.J.) test (catalase test using 30% H2O2) was used to differentiate Neisseria gonorrhoeae from other Neisseria species. A positive test was defined as immediate, brisk bubbling upon dropping 30% H2O2 onto a bacterial colony. One hundred percent of the gonococci were Superoxol positive. Only 1% of Superoxol-positive isolates on Thayer-Martin agar were organisms other than gonococci (99% specificity). The test was more reliable than the coagglutination test. Individual strains of a wide variety of Neisseria and Branhamella species were Superoxol positive. They could usually be differentiated from N. gonorrhoeae by their poor growth on selective media, colonial morphology on nonselective media, and simple biochemical tests. The Superoxol test is an excellent screening test for N. gonorrhoeae. A positive result on a clinical isolate growing on Thayer-Martin agar is strongly suggestive of the presence of gonococci.