In order to study the carrier rate and immunity to Group B streptococcus (GBS) of unmarried women, an urinary culture was taken and blood serum was assayed by ELISA for type-specific antibody in female students. Heretofore there have been very few reports about GBS in unmarried women in Japan. The validity of urinary culture as a substitute for vaginal culture was initially studied. The carriage of GBS was evaluated by vaginal, anal and urinary cultures in 90 pregnant women. Carrier detection were 18 carriers (20.0%) by vaginal culture, 22 carriers (24.4%) by anal culture and 18 carriers (20.0%) by urinary culture. Fifteen of the 18 subjects (83.3%) detected as carriers by vaginal culture carried the same strain of GBS in urine. Therefore, an urinary culture appears to perform as well as the vaginal culture as a convenient test for GBS. Nineteen (16.2%) of 117 unmarried women had positive urinary cultures for GBS. Among the 19 with positive cultures for GBS, 3 (15.8%) were type Ia, 3 (15.8%) were type Ib, 8 (42.0%) were type III and 5 (26.4%) were other types. Type II was not detected. From the type-specific antibody assay, the histogram of ODI (optimal density index) frequency of types Ia, Ib and III showed a concentration in a relatively narrow range at low ODI, while that of type II was dispersed over a relatively wide range.