We have evaluated the potential relationships between plasma levels of certain coagulation factors, i.e. factor VII antigen (F VIIag) and factor VII coagulant activity (F VIIc), and parameters of lipid transport in a group of 90 normotriglyceridemic patients displaying hypercholesterolemia (Fredrickson's type IIa hyperlipoproteinemia). Levels of factor VIIc were significantly elevated (P less than 0.01) in this patient group as compared to a group of healthy normolipidemic subjects. By contrast, levels of factor VIIag were also increased, but such differences were not significant in relation to those of controls. Furthermore, concentrations of F VIIc and F VIIag in hypercholesterolemic males and females resembled each other. Similar observations were made when patients were divided into those either presenting or lacking symptoms of vascular disease. However, plasma levels of both F VIIc and F VIIag were positively correlated with circulating triglyceride concentrations in the hypercholesterolemic group, but not with other parameters of lipid transport such as serum cholesterol, HDL-cholesterol, and apolipoprotein B. When patients were treated with a lipid-lowering agent (cholestyramine), lower levels of both F VIIc and F VIIag were found concomitantly with a decrease of similar order in triglyceride concentrations. We conclude that serum triglyceride levels, even within the normal range, may be associated with elevation in the activity of factor VII in hypercholesterolemic patients, thereby increasing their risk of thrombosis.