Objective: The aim of the present study was to determine whether postprandial concentrations of the active component of serine protease coagulation factor VII (VIIa) were lowered by acute boron supplementation in vivo. Design: An acute, randomized, placebo-controlled, double blind, cross-over study. Setting: Free-living population. Subjects: Fifteen apparently healthy men, aged 45 -65 y. Interventions: Subjects visited the centre on two occasions, with the study days separated by a minimum of 2 weeks. Following collection of a fasting blood sample, subjects received either placebo or acute bolus of 11.6 mg boron (given as 102.6 mg sodium tetraborate decahydrate) together with a standard fat-rich meal. Blood samples were obtained at 1, 2, 4 and 6 h after the administration of the test meal, during which time subjects were at liberty to consume deionized water only. Blood samples were assayed for concentrations of insulin, glucose, lipids and boron. Measurement of the concentration of activated factor VIIa and of factor VII antigen, and of the activity of coagulation factors VII, IX and X was also carried out. Results: Plasma boron concentrations were significantly higher following consumption of the boron supplement compared with placebo (0.124 AE 0.02 vs 0.008 AE 0.01 mg=l; P 0.001). There was no significant effect of acute boron supplementation on plasma insulin and glucose concentration or on blood lipid or coagulation factor profile. Factor VIIa rose significantly following consumption of the high fat meal (1.05 AE 0.07 vs 1.26 AE 0.07; P 0.001), but this increase was not altered by boron supplementation. Conclusions: Results from this study suggest that acute boron supplementation (at 11.6 mg boron) does not alter the activity of factor VIIa following consumption of a high-fat meal.