In order to investigate the neonatal infection of group B streptococci (GBS), vaginal and anal cultures, and measurement of type-specific antibodies to GBS were carried out on 461 pregnant women. Levels of antibody to GBS were measured with ELISA plates coated with type-specific antigen of GBS. These plates were furnished by Toyo Jozo Co., Ltd. The results were as follows: 1) Antibodies to type Ia, Ib, II and III were detected in 41.9, 34.7, 31.7 and 40.1% of subjects, respectively. 2) GBS was isolated in 78 (16.9%) of subjects. 3) Antibody levels against GBS in the sera of colonized mothers and cord blood of their infants were well correlated. 4) Among the colonized mothers, 4 out of 19 (Ia), 9 out of 18 (Ib) 5 out of 8 (II) and 5 out of 17 (III) showed low levels of antibody. 5) Those who had low levels of antibody were administered antibiotic delivery, and there was no case of crisis in both treatment (antibody levels were negative) and non-treatment (antibody levels were positive) groups.