Carboxyhaemoglobin (COHb%) and gamma-glutamyl-transferase (GGT) are today frequently used as objective indicators of tobacco and alcohol consumption. The relationships between COHb%, GGT and relative body weight, cholesterol, triglyceride and apolipoprotein AI (Apo-AI) were studied in middle-aged men attending a preventive medical programme in Malmö, Sweden. Although statistically significant the influence of COHb% on cholesterol and triglyceride was found to be clinically insignificant. GGT and body weight had, independent of each other, a significant influence on cholesterol and triglyceride. GGT was found to have a positive correlation to Apo-AI whereas body weight was found to have a negative correlation to Apo-AI. Four per cent of the cholesterol variability, 16% of the triglyceride variability and about 10% of the variability in Apo-AI could, in this study, be accounted for by COHb%, GGT and relative body weight.