BACKGROUND: The purpose of this study was to examine the causes and pathologic process of chronic non-productive cough as an isolated symptom with a normal spirometry and chest radiograph by investigating clinicopathologic findings. METHOD: We studied 25 adults with chronic non-productive cough over a 3-week period with a normal chest radiograph and pulmonary function tests without any other symptoms. Clinical assessment, cough score, chest and sinus radiograph, pulmonary function tests, methacholine challenge, allergic skin prick test, and bronchoscopy for bronchial biopsies were performed. Subjects were then treated with prednesolone 20 to 30 mg/day for 1 to 2 weeks. RESULTS: The experimental group was divided into two subgroups - those infiltrated with eosinophils, and those infiltrated with lymphocytes depending on eosinophil and lymphocyte counts, both of which were respectively higher than those of the control group. Eosinophils infiltrated group had mean numbers of eosinophil of 89.8 cells/mm(2) while control group's mean was 0.4 cells/mm(2)(P=0.005). Lymphocyte infiltrated group was 4 patients whose mean was 84.3 cells/mm(2) with 28.4 cells/mm(2) of control group(P=0.026). In addition, the mean thickeness of the basement membrane of experimental group was 14.20+/-5.20microM in contrast of control group whose mean was 3.50+/-1.37microM(P=0.001). With the methacholine challenge test, 7 of the 21 eosinophil infiltrated subjects were diagnosed with cough asthma; the other 14 with eosinophilic bronchitis. Three subjects with eosinophilic bronchitis were atopic positive(21.4%) with the skin prick test. In the lymphocyte dominant group, all four subjects were diagnosed with lymphocytic bronchitis. Cough score was improved after steroid treatment in 22 of 25 subjects in the experimental group (88.0%). CONCLUSION: These results suggest chronic non-productive cough as an isolated symptom with a normal spirometry and chest radiograph was associated with airway inflammation by eosinophil and lymphocyte infiltration. The causes for chronic non-productive cough were eosinophilic bronchitis, cough variant asthma, and lymphocytic bronchitis(written in frequency). They further suggest that therapeutic treatment with steroids can provide effective symptomatic relief.