OBJECTIVE: Our purpose was to assess the incidence of hyperhomocysteinemia in patients with a history of preeclampsia or fetal growth restriction, to evaluate the effects of vitamin supplementation on the methio-nine loading test, and to study the course of subsequent pregnancies in women with hyperhomocysteinemia and a history of preeclampsia or fetal growth restriction. STUDY DESIGN: A total of 207 consecutive patients with a history of preeclampsia or fetal growth restriction was tested for hyperhomocysteinemia. Thirty-seven were found to be positive and were treated with folic acid and vitamin B 6, and 27 had a second methionine loading test after vitamin supplementation. Fourteen patients became pregnant again while receiving vitamins and aspirin. RESULTS: All patients who underwent a methionine loading test after vitamin supplementation had a completely normalized methionine loading test. Of the 14 pregnancies in women receiving vitamins and aspirin, 7 were complicated by preeclampsia. Birth weights were 2867 ± 648 g compared with 1088 ± 570 g in the previous pregnancies. CONCLUSIONS: Vitamin B 6 and folic acid correct the methionine loading test in patients with hyperhomocysteinemia. Perinatal outcome in patients with a history of preeclampsia or fetal growth restriction and hyperhomocysteinemia appears to be favorable. (Am J Obstet Gynecol 1998;179:135-9.)