The occurrence of sputum eosinophilia was investigated in 115 patients with chronic bronchitis and asthma. They were clinically divided into four groups; those with asthma only, those with asthma of equal or greater duration than chronic bronchitis, those with chronic bronchitis recently complicated by asthma and those with chronic bronchitis only. Although sputum eosinophilia was more common in the asthmatic groups there was no significant difference between the groups in the degree of sputum eosinophilia. When the groups were subdivided on the basis of methacholine and isoprenaline response (asthma subgroup, greater than or equal to 20% response to isoprenaline or greater than or equal to 40% response to methacholine; chronic-bronchitis subgroup, less than 10% response to isoprenaline plus less than 20% response to methacholine), there was a significant difference between the groups in the degree of sputum eosinophilia. However, sputum eosinophilia still occurred in the chronic bronchitics. In the asthmatic patients, there appeared to be no difference in the degree of sputum eosinophilia in those with positive skin tests, or on steroid medication, compared with those with negative skin tests or not on steroids.¿