To examine the extent to which obstetric providers abide by prenatal practice guidelines published by ACOG. The prenatal records were abstracted for low-risk patients initiating care with randomly selected urban obstetrician-gynecologists, rural obstetrician-gynecologists, urban family physicians, rural family physicians, and urban certified nurse-midwives in Washington state between September 1, 1988 and August 30, 1989. The prenatal care recorded in their medical charts was compared with the ACOG-recommended guidelines. Overall, providers of all five types adhered closely to the published standards. Certified nurse-midwives recorded a standard of practice that most closely matched that recommended by ACOG. Overall, there was less complete adherence in the recording of maternal height, fetal activity after 30 weeks' gestation, and fetal presentation at or after 36 weeks' gestation. Those laboratory tests that ACOG has recommended most recently (serum alpha-fetoprotein and diabetes screening) and those not recommended for routine use were ordered less often on average by providers. The cross-sectional nature of this study cannot demonstrate definitively that ACOG's guidelines have changed provider prenatal practices. However, these findings demonstrate that providers in varying specialties and geographic locations can adhere to a detailed set of clinical guidelines if they are appropriately disseminated and implemented.