Bronchial tissues from 19 patients with asthma and 62 patients without asthma were examined using immunofluorescent technique. Antisera to human IgE, G, A, M, β 1 C-globulin, albumin, and fibrinogen were used. The patients with asthma were classified on the basis of skin test reactivity, frequency of symptoms, and correlation of symptoms with skin tests. In 11 of the 19 asthmatic patients one or more of the immunoglobulins G, A, or M were found in a characteristic location in the thickened bronchial basement membrane. The fluorescence of the gamma globulins was usually diffuse. In 4 cases, however, the fluorescence was granular. Many immunoglobulin-containing mononuclear cells (lymphocytes and plasma cells) were found in the submucosa of the bronchial specimens. The largest numbers of IgE-containing cells were seen in the specimens from the nonasthmatic patients showing inflammation. These nonasthmatic cases also had the largest numbers of cells containing IgA, G, and M. We were not able to distinguish the skin test-positive individuals from those with negative skin tests on the basis of the number of IgE-containing mononuclear cells in bronchial tissues, but there was only one patient with a simple seasonal history with good correlation of symptoms. Possible reasons for the infrequency with which IgE was found in the asthmatic patients were noted.