Countercurrent immunoelectrophoresis was used for detection of group- and type-specific antigens in body fluids of 61 infants from St. Louis and Indiana [USA] with group B streptococcal infections. Urine concentrated using an Amicon filter yielded the highest percentage of positive results; 81% were positive in the St. Louis group. When 3 body fluids (urine, CSF and blood) were available, at least 1 was positive for group B Streptococcus in 95% of the cases. The applicability of this test was demonstrated in a tertiary care facility (St. Louis) and in smaller hospitals (Indiana) with access to a central laboratory.