We have compared an enzyme immunoassay (ICON Step B, Hybritech) with cultures for demonstration of genital carriage of group B streptococci (GBS) in pregnant women, and studied the relationship between vaginal and rectal carriage of this organism. Pertinent literature has also been reviewed. Two hundred pregnant women at gestational week 17 were included. Swabs from the uterine cervix were tested for GBS by ICON Strep B immunoassay and ordinary cultures on blood agar. Additional swabs from the rectum were tested by cultures. The percentage of women with GBS in cervical secretions was 13.5% (27/200) by cultures and 4% (8/200) by the ICON Strep B immunoassay. The overall sensitivity of the immunoassay was 7.4%, and the specificity 96.5%. In conclusion, the sensitivity of rapid enzyme immunoassays is too low for accurate screening of GBS in the genital tract of pregnant women.