The prolonged incubation of dilute plasma on ice in the presence of added sulphatide vesicles or the long-chain saturated fatty acids (FA) stearic acid (C18:0) or behenic acid (C22:0) induced a concentration-dependent increase in factor VII coagulant activity (VIIc). The addition of FA at various ratios to human serum albumin showed the micellar non-bound pool to be responsible for this effect, FA bound to the high-affinity or low-affinity binding sites of albumin having no influence on VIIc. Plasma VIIc also increased following addition of behenate-enriched lipoprotein particles produced by incubation of the d < 1.006 g/ml lipoprotein fraction with this FA, or addition of lipoprotein remnants produced by pre-incubation of the d < 1.006 g/ml fraction with lipoprotein lipase. Long-chain saturated fatty acids in the interface of lipoprotein remnants, produced by the interaction of triglyceride-rich lipoprotein particles with lipoprotein lipase, appear to provide a surface that activates the contact system of coagulation and subsequently factor VII.