In the United States, group B streptococcus (GBS) is the leading cause of serious bacterial infections in newborns. In 1996, consensus guidelines for use of intrapartum antibiotic prophylaxis (IAP) to prevent perinatal GBS disease recommended either of two methods for identifying candidates for chemoprophylaxis: 1) late prenatal culture-based screening for GBS colonization or 2) monitoring of women intrapartum for particular risk factors associated with early-onset GBS disease. Evidence that culture-based screening was substantially more effective than the risk-based approach led to revised guidelines in 2002 recommending late prenatal GBS screening for all pregnant women. Although methods for isolation and identification of GBS from prenatal specimens remained the same as those recommended in 1996, the 2002 guidelines recommended that laboratories perform antimicrobial susceptibility testing on prenatal GBS isolates from women at high risk for penicillin anaphylaxis and clarified that laboratories should report the presence of any GBS in urine specimens from pregnant women. To assess laboratory adherence to recommendations in the 2002 guidelines, CDC's Active Bacterial Core surveillance (ABCs)/Emerging Infections Program Network surveyed clinical laboratories about prenatal culture-processing practices in 2003. This report summarizes the results of that survey, which indicated that, although adherence to GBS isolation procedures was high, opportunities exist to improve implementation of recommendations related to antimicrobial susceptibility testing and GBS bacteriuria.