During 1983, 38 patients with pregnancy-induced hypertension were treated with hydralazine-apresoline (1-hydrazinophthalazine). During the course of their treatment, five of these patients showed evidence of the HELLP syndrome described by Weinstein (hemolysis, thrombocytopenia, and elevated liver enzymes). Evidence is presented on the role of hydralazine in producing hepatocellular damage. Liver function is compromised during the natural course of pregnancy-induced hypertension, and 5-10% of preeclamptic patients develop the HELLP syndrome. In many places hydralazine is the drug of choice in the treatment of pregnancy-induced hypertension.