The sputum differential eosinophil/neutrophil count was done in 384 patients using Leishman staining. The patients were distributed in four groups: bronchial asthma (197 patients); chronic bronchitis with wheezing (45 patients); chronic bronchitis and/or emphysema without wheezing (73 patients); other pulmonary diseases (64 patients). Eosinophils were present in patients from all groups but more frequently (P less than 0.001) in asthma: 142 (72%) of 197 patients. In bronchial asthma and chronic bronchitis with wheezing the percentages of eosinophils were more frequently (P less than 0.001) above 80%: 57% and 58% of the patients respectively. The other two groups had more cases with 19% or less eosinophils. There is no percentage level specific for asthma but levels above 80% of eosinophils are strongly suggestive of asthma or of chronic bronchitis with wheezing.