OBJECTIVE: The effects of two antihypertensive drugs, methyldopa and isradipine, on fetal heart rate pattern were analyzed by computerized cardiotocography. STUDY DESIGN: The first part of the study was a prospective, randomized, controlled trial of 19 women with preeclampsia in the third trimester given 2.5 mg of oral slow-release isradipine twice a day or 250 mg of methyldopa three times a day. In a second part of the study 23 women with preeelampsia in the third trimester given 5 mg of oral slow-release isradipine twice a day were compared with 23 matched controls without medication. Main outcome measures were maternal blood pressure and mean baseline fetal heart rate, fetal movements, number of accelerations, periods of high and low baseline variability, and mean baseline heart rate variability. RESULTS: Compared with the pretreatment value, the mean arterial blood pressure decreased significantly in all drug treatment groups. Fetal heart rate characteristics were not significantly changed during drug treatment or bed rest. CONCLUSION: The various features of the fetal heart rate pattern evaluated by computerized methods were not influenced by treatment with methyldopa or isradipine.