Fibrinogen is considered to be a strong predictor and independent factor of cardiovascular diseases. The data presented here describe the baseline measurements of fibrinogen in 1008 apparently healthy subjects, aged 4-60 years and their relationship to age, sex, body weight, smoking, alcohol, and use of oral contraceptives. Pearson's correlations and a linear multiple regression model were used. Plasma fibrinogen was measured kinetically in a photometer, the Behring Chromotimer, using the CTS-fibrinogen method. There were neither statistical difference between girls and boys aged 4-20 years nor correlation with variables related to cardiovascular diseases. In adults, we found an increase of plasma fibrinogen concentration with age and no statistical difference between men and women, except in subjects aged 40-50 years. There was a positive correlation between fibrinogen and ponderal index. In women aged 20-30, 30-40, 40-50 and 50-60 years, the mean fibrinogen concentrations increased of 0.009, 0.021, 0.010 and 0.015 g/l for one percent of overweight, in each subgroup respectively. In women aged 20-30 years using oral contraceptives, the mean fibrinogen concentration was 0.19 g/l higher than in women not using oral contraceptives. The smoking effect was observed only in 30-40 year-old men. Each cigarette smoked per day increases of the mean fibrinogen by 0.35 g/l after standardization for ponderal index and alcohol consumption. Alcohol consumption was negatively correlated to plasma fibrinogen in subjects 30-40 years old. In women, 1 g of alcohol per day induces a 0.008 g/l decrease in the mean fibrinogen while in men the decrease is 0.004 g/l.(ABSTRACT TRUNCATED AT 250 WORDS)