Bronchi biopsy specimens of 42 patients with chronic respiratory diseases were studied for immunoglobulin-containing cells, using an indirect immunoperoxidase technique. The number of immunocytes was expressed per unit tissue section surface. The cells were located directly under the epithelium. In most biopsy specimens IgA-, IgG- and IgM-containing cells were demonstrable, with IgA- and IgG-containing cells in the majority. IgE-containing cells were found only in small numbers in biopsy specimens of a few patients. The presence of IgE-containing cells was nearly always accompanied by a high amount of mast cell-bound IgE in the bronchial mucosa. No correlation could be found between the number and class of immunocytes and clinical data.