Most of the 150 Streptococcus suis isolates from pigs and ruminants used in this study grew under aerobic conditions and were α-hemolytic on sheep blood agar. Part of the cultures required an increased CO2 concentration. These cultures, representing the CO2-dependent ecovar of S. suis, were mainly β-hemolytic on sheep and horse blood agar and gave a synergistic hemolytic reaction with staphylococcal β-lysin. Similar to S. suis reference cultures, the routine isolates showed typical biochemical properties of this species. Few cultures, mostly those from ruminants, could be classified as the sorbitol and mannitolpositive ecovar. Formamide extracts of 81% of the cultures reacted with group D-specific antisera. Serotyping of the S. suis isolates revealed mainly capsular types 2, 1/2, 1, 5, 11, 13, 23, 3 and 15. The determination of antibiotic susceptibility revealed a high number of cultures to be resistant to clindamycin, erythromycin, kanamycin, neomycin, streptomycin and tetracycline. Cultural, biochemical and serological properties together with antibiotic resistance patterns could be used to characterize individual isolates of S. suis. This could be of importance in epidemiological studies.