SummaryOne hundred and sixty three isolates of group B streptococci from human carrier and disease conditions in Brisbane, Melbourne and Adelaide were serotyped by the Lancefield capillary precipitin test, coagglutination and microimmunodiffusion. Serotypes I and III were most common; serotype III appeared to occur uniformly but serotype Ia varied in distribution. No significant difference was found in serotype distribution among isolates from pregnant and non‐pregnant women, or rectal and vaginal swabs; however, type Ia was found to occur significantly more often as an infectious agent than as a commensal (P<0.01).