We examined patterns of airway response of thirty nine asthma patients who had positive responses on allergen inhalation tests. Six types of inhaled allergens were used: house dust mite, animal, pollen, plant, mold, and others. Three patterns of responses were found: isolated immediate asthmatic response (IAR), immediate and late response (Dual), and isolated late asthmatic response (LAR). No relationship was found between the pattern of response and pulmonary function, airway sensitivity, IgE RIST titers, numbers of eosinophils, or concentration of inhaled antigens. Animal antigens tended to cause a dual response, and molds did only rarely. Ten of 39 challenged patients had an isolated LAR, half of which were caused by mold antigen inhalation. RAST scores were lower in isolated LAR than in other responses. Changes in the number and proportion of peripheral leukocytes during the challenge tests were also studied. Total leukocyte count had increased significantly in the isolated LAR group by 24 hours after the inhalation. These results suggest that the pattern of airway response after inhalation depended in part on the type of inhaled antigen, and that non-IgE mediated immune reactions have some role in the isolated LAR.