To investigate the existence of an association between haptoglobin (Hp) genotypes and the severity of heart complications in Chagas' disease. Hp genotyping was performed by PCR in 107 Brazilian patients sub-classified in asymptomatic, with mild heart disease and with severe heart disease. Multiple logistic regression (R(2)=24%) indicated that patients with the Hp1-1 genotype have lower probability of developing the severe heart complications. The Hp polymorphism may influence the clinical evolution of Chagas' disease.43314-6