Studies at two Brown Medical School-affiliated hospitals were undertaken to evaluate a new selective broth medium (GBS broth) and to compare it to the LIM broth currently used to culture for group B streptococci. Beta-hemolytic group B streptococci produce a carotenoid pigment that turns GBS broth an orange color. From a total of 580 pregnant women, duplicate vaginal-rectal swabs were collected at 35 to 37 weeks of gestation and cultured for group B streptococci, using either LIM broth (a selective broth containing antibiotics) or GBS broth for enrichment. Specimens were either transported to the laboratory or immediately placed in the respective enrichment broths and delivered to the laboratory. GBS broth medium had sensitivity, specificity, and positive and negative predictive values of 87.8, 100, 100, and 95.1% when planted in the laboratory and 90.3, 100, 100 and 97.6%, respectively, when inoculated at bedside. Use of GBS broth would satisfy Centers for Disease Control and Prevention requirements and would provide faster, more-sensitive, and cost-effective detection of group B streptococci in pregnant women.Group B streptococci (GBS) cause serious, life-threatening infections in the newborn. Mortality of GBS sepsis in neonates may exceed 50%, and preterm infants are especially at risk. Intrapartum prophylaxis for pregnant women colonized with GBS has been recommended for several years, since clinical trials showed that the administration of antibiotics to women in labor had a drastic effect in reducing early-onset invasive GBS infection in the neonate (1). Centers for Disease Control and Prevention guidelines issued in 2002 (2, 3) recommend that all pregnant women be screened for vaginal-rectal colonization with GBS at 35 to 37 weeks of gestation. These new guidelines for predelivery testing of pregnant women may have a significant impact on clinical microbiology laboratories, which may expect to see an increase in the volume of test requests for GBS screening for pregnant women. The recommended method for detecting carriage of GBS in pregnant women is to use a selective enrichment broth medium with subsequent subculture on a sheep blood agar plate (BAP) (3). Some laboratories inoculate a BAP before placing the swab in the enrichment broth. The enrichment broth is subcultured only if the primary BAP is negative. A more rapid, less labor-intensive, and more cost-effective method than the traditional culture is needed to screen patients for GBS colonization. Granada medium has long been used in Europe to detect GBS in pregnant women. Strains of beta-hemolytic GBS produce a carotenoid pigment, visible as an orange color, in this medium, usually within 24 h. Variable results on the sensitivity of this medium have been reported, with some investigators considering it to be unacceptably low (4, 5). A new, improved enrichment broth, modified from the original Granada medium, called GBS broth, is now also available (7). This medium has the advantage of reducing both incubation and technical time. Our studies were un...