Histamine-binding proteins have been isolated from healthy subjects and patients with endogenous bronchial asthma. Histaminopectic properties were exhibited mainly by IgA, IgG, IgM immunoglobulins, orosomucoid, albumin and ceruloplasmin. Quantitative determination of the identified proteins showed that in the control group immunoglobulins bound histamine in 97.5%, whereas in asthmatics the corresponding percentage (about 81%) was statistically significantly lower.