Background: Eotaxin is a chemokine specific for eosinophils and may play an important role in eosinophil recruitment in asthma. The effects of eotaxin inhalation on sputum and blood eosinophils, exhaled nitric oxide (NO), and bronchial responsiveness were determined. Methods: Eotaxin was administered by nebulisation to asthma patients in three studies: (1) an open dose finding study with eotaxin (5, 10 and 20 μg) to two asthmatic subjects; (2) a randomised placebo controlled study with 20 μg eotaxin to five asthmatic subjects and five normal volunteers; and (3) a randomised placebo controlled study with 40 μg eotaxin to nine asthmatics. Forced expiratory volume in 1 second (FEV 1), exhaled NO, and blood eosinophils were measured before and hourly for 5 hours after nebulisation and at 24 and 72 hours. Methacholine bronchial challenge and sputum induction were performed before and at 5, 24, and 72 hours after nebulisation. Results: In the two placebo controlled studies there was no change in sputum eosinophil count and sputum eosinophilic cationic protein concentration after eotaxin inhalation compared with placebo. FEV1, exhaled NO, and methacholine PC20 did not change. However, high dose eotaxin (40 μg) induced an increase in sputum neutrophil count compared with placebo (p<0.05). Conclusions: Inhaled eotaxin up to 40 μg induced no changes in sputum eosinophil count but at 40 μg it increased the sputum neutrophil count. The significance of this finding is unknown.