The gene for NAD-glycohydrolase (nga) of group A streptococci (Streptococcus pyogenes) was identified and shown to be located immediately adjacent to the gene for streptolysin O (slo). The nga gene contains 1341 base pairs and encodes a protein of 447 amino acids, including an N-terminal signal peptide. Results from analysis with the polymerase chain reaction indicated that the nga gene is present in all of the strains tested. Functional extracellular NAD-glycohydrolase, also known as NADase, was detected among a wide variety of clinical isolates and known laboratory strains and shown to be present in 72% of 100 strains examined. In contrast, 92% of strains isolated from patients with invasive streptococcal infections were positive for NADase production.