Serum levels of carbohydrate-deficient transferrin (CDT), the proportions of eight haemoglobin fractions separated by cation exchange liquid chromatography, indices of liver function and various haematological parameters were determined in most of a group of 49 chronic alcoholics who had misused alcohol for at least the preceding 3 months and in 15 healthy non-alcoholic control subjects. The percentages of alcoholics giving abnormally high values for gamma-glutamyl transferase (GGT) activity, CDT levels, GGT activity or CDT levels or both, and aspartate aminotransferase (AST) activity were, respectively, 73.0, 71.0, 87.1 and 64.4. The percentages of patients giving abnormally high values for the proportion of HbA1a, proportion of HbA1ach, proportion of HbA1a or HbA1ach or both, MCH, MCV and red cell distribution width (RDW) were, respectively, 46.8, 25.5, 55.3, 55.3, 36.2 and 29.8. Reduced values for the red cell folate concentration, lymphocyte count and platelet count were found in 36.2%, 6.4% and 17.0%, respectively, of the alcoholics. When compared with the control subjects, the group of alcoholics showed statistically significant increases in the mean values for the MCV, MCH, MCHC and RDW and statistically significant decreases in the mean values for the haemoglobin distribution width (HDW) and the logarithms of the holo-transcobalamin II concentrations and the platelet count. The logarithms of the CDT values correlated directly with the MCV and MCH and inversely with the logarithms of the lymphocyte or platelet counts and the HDW, suggesting but not proving that the haematological changes in chronic alcoholism may be at least partly related to defective glycosylation of the constituents of developing blood cells or, possibly, of haemopoietic growth factors.(ABSTRACT TRUNCATED AT 250 WORDS)