The plasma levels of beta-thromboglobulin (BTG) and platelet factor 4 (PF-4) were measured in patients during the normal obstetric period and in preeclampsia. A significant increase was observed in the two proteins with respect to the nonpregnant control group. Both proteins increased significantly with preeclampsia and a further increment was observed with the severity of preeclampsia though no significant difference in PF-4 levels was encountered between pregnant and mildly preeclamptic women. There was no correlation between BTG, PF-4 and thrombocyte counts.