The effect of prostaglandin E1 (PGE1) on liver dysfunction due to high-dose methotrexate (HD-MTX) was investigated in children with malignant diseases. Eight children received 45 doses of HD-MTX. Group 1 (33 cases) received no PGE1. Group 2 (4 cases) received PGE1 intravenously 8 times every 12 hours for 3 consecutive days. Group 3 (8 cases) received infusion of PGE1 continuously for 4 days (1 day before and 3 consecutive days after MTX infusion). No significant difference was observed among the serum levels of transaminase in these 3 groups as well as the corresponding levels in the same patients who were treated with or without PGE1. There are reports suggesting that in spite of the lack of any difference in serum transaminase levels in rats with drug-induced hepatic injury given PGE1 infusion, data on DNA synthesis and survival ratio indicate the existence of 'hepatocytoprotection'. Further investigation will be necessary in order to decide whether PGE1 infusion is indeed effective.