Factor-VII levels were measured in members of an industrial population participating in a long-term prospective study of arterial disease. A modified semi-automated method with an artificially prepared factor-VII deficient plasma, one batch of freeze-dried thromboplastin and one freeze-dried pooled reference plasma was used throughout. All calculations were carried out on a programmable desk calculator.Mean factor-VII levels in men and in women never on oral contraceptives were similar (age-adjusted means 95.0% and 92.4% respectively). A very highly significant increase in factor VII was found in women on the low oestrogen contraceptive pill (age-adjusted mean 134.8% compared to 92.4% in women never on oral contraceptives).There was a highly significant rise in factor-VII activity with age in both men and women. In men, factor VII rose 0.45% per year, whereas in women it increased at the rate of 1.1% per year. The difference in the slopes of these regression lines for men and women was significant. At younger ages, the mean levels for women were lower than for men, while at older ages the reverse was true.No relationship with ABO blood groups or secretor status were found. Venepunctures noted as difficult appeared to have no effect on factor-VII levels.Factor VII is the coagulation factor required for the activation of factor X with tissue extracts. Increased levels of factor VII are described in pregnancy (Alexander et al, 1956;Rutherford et al, 1964; Amris & Starup, 1967) and in women on oral contraceptives (Rutherford et al,