Interleukin 8 (IL-8) is a chemoattractant cytokine having a distinct target specificity for the neutrophil. However, it was also found to be active on primed eosinophils. IL-8 was measured by enzyme immunoassay in the bronchoalveolar lavage fluid (BALF) of 9 control subjects, 19 asthmatics and 36 chronic bronchitis patients. Its levels were correlated with neutrophil and eosinophil counts as well as levels of myeloperoxidase (MPO) and eosinophil cationic protein in the BALF. Asthmatic and chronic bronchitis patients had elevated levels of IL-8 in comparison with normal subjects. There was no correlation between the severity of asthma or chronic bronchitis and IL-8 levels. In asthmatic subjects there was a correlation between IL-8 and MPO levels (p < 0.0001, Spearman test). There was no significant correlation between eosinophils and IL-8. In chronic bronchitis there was a correlation between IL-8 and MPO levels as well as between IL-8 and neutrophil counts (p < 0.004 and p < 0.0152, respectively, Spearman test). IL-8 is involved in neutrophilic inflammation in asthma and chronic bronchitis, but differences in the IL-8 regulation of neutrophils were observed in both diseases.