We examined the pattern and degree of the inflammatory process in bronchial biopsy specimens taken by fiberoptic bronchoscopy in eight asthmatic subjects (two women aged 19-38 years) after 5 years of specific immunotherapy (SIT) to mite extracts (SIT group). At the time of study, they received a maintenance dose of mite-extracts (last subcutaneous administration 3 weeks before bronchoscopy). Results were compared with those found in eight matched mite-sensitive subjects with stable asthma (two women aged 19-36 years; non-SIT group) and in eight healthy individuals (four women aged 22-29 years; control group). Bronchial biopsy specimens were fixed in periodate-lysine-paraformaldehyde, embedded in glycol methacrylate, and stained with hematoxylin-eosin and 2% toluidine blue. Number of eosinophils, mast cells, and total nucleated cells were counted separately in the epithelium and lamina propria by light microscopy and expressed as cells/high power field. Within the epithelium, eosinophil and mast cell counts in SIT and non-SIT groups were significantly higher compared to controls, whereas total cell counts were not statistically different. Within the lamina propria, total cell count in SIT and non-SIT groups was significantly higher compared with the control group, whereas mast cells were similar. The number of eosinophils in both SIT and non-SIT groups was higher compared with controls; however this reached statistical significance only in SIT-groups. Comparison between the two groups of asthmatics did not show any significant difference for any cell counts.(ABSTRACT TRUNCATED AT 250 WORDS)