Pseudoephedrine, a stereoisomer of ephedrine with alpha- and beta-adrenergic properties, is the active ingredient in over-the-counter oral decongestants. Its safety during pregnancy has not been studied adequately. The purpose of this investigation was to evaluate the effects of pseudoephedrine on uterine and fetal Doppler blood flows. Twelve healthy pregnant women between 26-40 weeks' gestation ingested a standard 60-mg dose of pseudoephedrine. A pulsed Doppler system was used to perform blood flow measurements of the uterine arcuate artery, fetal aorta, and umbilical artery before dosing, immediately thereafter, and at 15-minute intervals during the first 3 hours after drug ingestion. Blood flow velocities were not altered significantly after dosing in either the maternal or fetal circulation. In no case did absolute fetal or uterine blood flow velocities decrease significantly or systolic/diastolic ratios persistently elevate to abnormal values. We conclude that no significant alterations in the uterine or fetal circulations occur after the ingestion of a single dose of oral pseudoephedrine by healthy pregnant patients in the third trimester.