This study describes prescription drug use before and during pregnancy and is based on data obtained from the paid Medicaid claims of 18,886 Michigan women aged 15 to 44 years who were delivered of a live infant. Rates of exposure to drugs within 15 therapeutic categories are presented for each of five 90-day periods preceding delivery. Overall dispensed drug use (excluding vitamins) decreased during pregnancy; however, there was still substantial exposure to drugs including drugs that are contraindicated during pregnancy. During the gestational period, study mothers received an average of 3.1 prescriptions for nonvitamin drugs. Black mothers received more exposure to drugs other than vitamins than did white mothers. Black mothers had higher rates of exposure to analgesics, ampicillin, codeine, and vaginal preparations. Similarities between black and white mothers in the use of vitamins with and without other drugs suggest there is no racial difference in attaining prenatal care within the Medicaid system, but that black mothers may have more medical problems that warrant the use of other medications in addition to vitamins during pregnancy.