In the present study 70 Streptococcus porcinus isolates could be identified and further characterized by cultural and biochemical properties, by determination of their antibiotic susceptibility and by serological classifications. The S. porcinus included serogroup- and serotype-reference strains, presumptive group candidates and isolates obtained from routine diagnostics. All cultures investigated appeared with a broad zone of beta-haemolysis on sheep blood agar showed a CAMP-like reactivity in the zone of staphylococcal beta-lysin and had the typical biochemical properties of this species. Determination of antibiotic susceptibility revealed a high number of cultures to be susceptible to ampicillin, bacitracin, chloramphenicol, penicillin and vancomycin. Resistances could be observed for erythromycin, minocycline, sulfamethoxazole-trimethoprim, streptomycin and tetracycline. Serogrouping and serotyping could be performed with autoclaved extracts of the bacteria and group- and type-specific antisera prepared against reference strains and group candidates by immunodiffusion reactions. By serogrouping almost all cultures could be classified into serogroup E, U, V or P. Some group E streptococci could additionally be serotyped with type II, VI, VII and group X specific antiserum indicating that group X represents an additional type antigen of serogroup E. None of the antigen preparations reacted with serotype IV, V or group candidate NG1 specific antiserum. The described properties might help to identify and further characterize isolates of the species. S. porcinus, possibly useful in epidemiological aspects.