To assess platelet changes in pregnant women with chronic glomerulonephritis (CGN) and essential hypertension (EH) we estimated platelet lactic dehydrogenase activity (LDH), beta-thromboglobulin and thromboxane B2 (TxB2) plasma levels and ADP-stimulated platelet aggregability. Five groups of gravidae (26-40 weeks of gestation) were studied: with EH (n = 20), with CGN and hypertension (n = 31), with CGN without hypertension (n = 29), with late toxemia (n = 11), nonpregnant CGN women (n = 10) and healthy pregnant women (n = 20). Activation of platelet function was found in gravidae with CGN and EH. Platelet disorders were especially pronounced in pregnant women with CGN and with EH, but they were less pronounced than in control group with late toxemia. We believe that hypertension is more important stimulating factor for platelet activation than renal disease. We suggest that platelet disorders in outpatients are brought about by endothelium damage caused by elevated blood pressure.