Information available in the literature was reviewed (10, 13, 32), and more recent isolates were tested to analyze these the serogroup data for S. porcinus and S. pseudoporcinus. The animal S. porcinus strains SS-995 and SS-996 cross-reacted with CDC group B antisera as well as with several commercial kits. In addition, the clinical isolate 1256-95, described as reacting with all commercial group B antisera, has subsequently been identified as S. pseudoporcinus. A noteworthy finding was that only two of the S. porcinus strains tested reacted with NG1 antisera, whereas almost all S. pseudoporcinus strains reacted.