The blood haemoglobin concentration is one of the most frequently used laboratory parameters in clinical practice. There is evidence that haemoglobin levels are influenced by tobacco smoking. The objective of this study was to evaluate the impact of smoking and alcohol consumption on haemoglobin concentrations in apparently healthy subjects living at sea level. A retrospective, epidemiological cohort study was performed in 1984. Participants were 1,503 men and 1,437 non-pregnant women evenly distributed in age cohorts of 30, 40, 50, and 60 years. Information of smoking habits and alcohol consumption were obtained by a questionnaire. Haemoglobin was measured in the fasting state on Coulter-S. Men displayed no difference in mean haemoglobin levels in the four age groups. In women, mean haemoglobin increased gradually with age (p = 0.001). Fifty-nine percent of men and 50% of women were daily smokers. Female smokers displayed a significant positive correlation between number of cigarettes/day and haemoglobin concentrations (r = 0.12, p = 0.002). Heavy smokers (more than ten cigarettes/day) had significantly higher mean haemoglobin (1.4% higher in men, on average 3.5% higher in women) than non-smokers (p < 0.01). Smokers demonstrated a significant correlation between cigarettes/day and drinks/week in men (r = 0.24, p < 0.001) and women (r = 0.16, p < 0.001). Non-smokers displayed a significant positive correlation between drinks/week and haemoglobin concentrations in men (r = 0.14, p = 0.001) and women (r = 0.08, p = 0.05). In non-smokers, alcohol consumption >14 drinks/week and more than seven drinks/week for men and women, respectively, increased mean haemoglobin by 1.3% in men and by average 1.9% in women compared with those consuming < or =14 and less than or equal to seven drinks/week. Smokers displayed similar results. Body mass index per se had no direct influence on haemoglobin levels but had indirect positive influence in men through its correlation with tobacco smoking and alcohol consumption. Tobacco smoking has an increasing effect on haemoglobin concentrations in both genders, which is proportional to the amount of tobacco smoked. The effect appears to be more pronounced in women. Likewise, high alcohol consumption has an increasing effect on haemoglobin in both genders, being most pronounced in women. However, in clinical biochemistry, the relatively small changes in haemoglobin do not justify the use of separate reference ranges in smokers and alcohol consumers.