Haptoglobin (Hp) groups were investigated in 148 patients with bronchial asthma. A significant (p less than 0.005) deviation from the expected Hardy-Weinberg equilibrium, with a decreased frequency of heterozygotes, was observed among patients with a family history of asthma. This deviation was more pronounced among patients with adult onset of asthma. The presence or absence of atopy had no significant influence on the phenotype distribution.