A study of 216 noncapsular strains of Neisseria meningitidis isolated from patients and carriers received in the Meningococcus Reference Laboratory between 1978 and 1984 is reported. The characterization of the strains consisted of biochemical tests for the following characteristics used for the differentiation of Neisseria species: oxidase, catalase, and beta-galactosidase activities; sugar degradation; nitrate and nitrite reduction; DNase activity; polysaccharide production with 5% sucrose; aminopeptidase activity; and growth in Thayer-Martin and Catlin media. Of the strains studied, 50 showed characteristics of a new taxon recently described (Neisseria polysacchareae). Characteristics that differentiated these strains from meningococcal isolates were polysaccharide production with 5% sucrose, gamma-glutamylaminopeptidase activity, and a requirement for cysteine or cystine for growth in Catlin medium. All of the N. polysacchareae strains identified were isolated from the nasopharynx of healthy carriers.