We studied the effect of inhaled specific antigen on airflow resistance, histamine concentration, and mast cell numbers in airway tissues in allergic dogs. In each of six allergic dogs with open chests, inhalation of specific antigen aerosol (Ascaris suum) increased airflow resistance from 0.30+/-0.40 (mean+/-SE) to 2.8+/-0.41 cmH2O/1 per s (P less than 0.05); decreased mast cell number from 38.6+/-3.2 to 24.3+/-4.5 mast cells/mm2 (P less than 0.05); decreased histamine (per mg airway tissue) from 5.3+/-0.4 to 3.5+/-0.2 ng (P less than 0.05) in lobar bronchi 5-7 mm in diam; and released histamine into the blood perfusing the lung, control arterial plasma histamine; 2.8+/-0.64 ng/ml; antigen: 154+/-1.7 ng/ml (P less than 0.005). Specific antigen caused no significant changes in mast cells or histamine in bronchi 1-2 mm in diam. Control aerosols of nonspecific antigen or methacholine did not change levels of mast cells or histamine in airway tissues. These results suggest that experimental canine asthma involves local airway reactions with degranulation of mast cells and histamine release, as well as vagally mediated reflex bronchoconstriction.