beta-Adducin plays a role in maintaining the structural integrity of the red blood cell (erythrocyte) membrane. Moreover, beta-adducin-deficient knock-out mice show a phenotype characterized by mild anaemia and compensated haemolysis. We therefore investigated whether, in humans, common haematological phenotypes of red blood cells were associated with a polymorphism in exon 15 of the human beta-adducin gene (C1797T). We studied 802 unrelated individuals and 294 families (459 parents and 609 offspring) randomly selected from a Caucasian population. We employed generalized estimating equations to allow for the non-independence of the observations within families, while controlling for co-variables. In 917 men, with adjustments applied for age, body mass index, serum total cholesterol, smoking and alcohol intake, CC homozygotes had significantly ( P =0.02) lower values for red blood cell count (4.93 x 10(12)/l compared with 4.86 x 10(12)/l), haemoglobin level (9.30 compared with 9.18 mmol/l) and haematocrit (45.0% compared with 44.4%) than T allele carriers. In the 329 men who consumed alcohol, the differences between CC homozygotes and T allele carriers were 0.13 x 10(12)/l ( P =0.02) for red blood cell count, 0.23 mmol/l ( P =0.005) for haemoglobin and 1.08% ( P =0.02) for haematocrit. In 953 women, none of these associations was significant ( P >/=0.06), regardless of alcohol intake [13.3% of women ( n =127) consmued alcohol]. In conclusion, in men consuming alcohol, the beta-adducin CC genotype was associated with lower red blood cell count, haemoglobin level and haematocrit. We hypothesize that, in CC homozygotes, alcohol consumption may unveil the greater fragility of the red blood cell membrane. This genotype may slightly potentiate the structural and functional haematological disturbances associated with alcohol intake.