The cholesterol:phospholipid ratio (C/PL) was measured in platelet plasma membrane in patients with pregnancy-induced hypertension [with proteinuria (PE), and without proteinuria (PIH)] and in matched normotensive gestational controls (NT). The C/PL was raised in the platelet membrane from PE (1.52 +/- 0.50, 95% CI 1.13 to 1.90) and PIH (1.38 +/- 0.34, 95% CI 1.08 to 1.67) compared with that from NT controls (0.88 +/- 0.13, 95% CI 0.80 to 0.95) (p less than 0.01, ANOVA test). No correlation was found when C/PL was regressed against total serum cholesterol levels. The abnormality of lipid composition of the platelet plasma membrane could account for some of the changes in platelet function that have been described in PIH.