We evaluated the usefulness of eosinophil cationic protein (ECP) in induced sputum and in serum as markers of asthmatic inflammation in children. We measured ECP in serum and in total induced sputum samples from 14 children (7-11 years) with newly detected asthma before and after treatment, and from ten healthy non atopic controls of the same age. The patients inhaled budesonide, 800 micrograms/m2/day for the first month and 400 micrograms/ m2/day for the next 5 months, both divided into two doses, and nedocromil, 4 mg three times daily for the following 6 months. In both sputum and serum, ECP levels were higher in the patients than in the controls, but the difference was more distinct in sputum. Significant clinical improvement during the treatment was accompanied by a decrease in sputum ECP, whereas serum ECP did not change. The results suggest that induced sputum is useful as a non invasive source material for evaluating asthmatic inflammation in children, total sputum ECP being more sensitive than serum ECP for diagnosing and monitoring asthma.