The association between a number of blood and serum quantities and industrial organic solvent exposure and poisoning, alcohol consumption, smoking, and age was analysed in 277 subjects by multiple regression analysis. Solvent poisoning was associated with changes in S-creatine kinase concentrate at the P less than 0.001 level (higher if exposed, lower if non-exposed at the examination time). Solvent exposure seemed to potentiate the effects of smoking on B-hemoglobin conc. and B-erythrocyte volume fraction, and the effect of age on S-creatinine conc. at the P less than 0.05 level, while there was no interaction between alcohol consumption and solvents. Alcohol consumption in itself, as well as smoking and age, were highly significantly associated with changes in a large number of blood and serum quantities. There was no difference in the alcohol markers (mean erythrocyte volume = MCV, S-alanine aminotransferase and S-urate) in patients with solvent poisoning compared to healthy volunteers. The results indicate that studies on the effects of solvents of haematology and biochemistry are not valid unless the effects of alcohol, smoking and age are established; and that excessive alcohol consumption is an unlikely explanation for the symptoms of patients with solvent poisoning. The findings suggest that smoking and age may have combined effects with solvents.