The phenotypic and genotypic characteristics of 25 Streptococcus porcinus isolates recovered from human sources were investigated and compared to the characteristics of 17 reference strains obtained from nonhuman sources. All of the S. porcinus isolates were beta-hemolytic (wide zones), susceptible to vancomycin, gave positive results for the leucine aminopeptidase and l-pyrrolidonylarylamidase tests, and produced acids from mannitol and sorbitol. Most of them were positive for the CAMP test and resistant to bacitracin. The isolates were susceptible to most of the 14 antimicrobials tested, except for tetracycline, for which 80% of the human isolates and 35.2% of the nonhuman strains were resistant. The tet(M) and the tet(O) genes were detected in 23 (88.5%) and 8 (30.8%) of the 26 tetracycline-resistant isolates, respectively. Analysis of whole-cell protein profiles obtained after sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a high similarity among the profiles. Chromosomal DNA was analyzed by pulsed-field gel electrophoresis (PFGE) after digestion with SmaI and by random(ly) amplified polymorphic DNA (RAPD)-PCR using primer 1254. Analysis of SmaI-restricted genomic DNA revealed the substantial genetic diversity among S. porcinus isolates from nonhuman sources, which were also serologically more diverse. Most of the human isolates belonged to serogroup NG1 and shared highly related PFGE profiles that were distinct from profiles of isolates from nonhuman sources. These results were in agreement with those obtained by analysis of amplicons after RAPD-PCR, indicating the potential ability of these techniques for typing S. porcinus and suggesting the occurrence of a few clonal groups of S. porcinus strains adapted to the human host.