Objeetive.'We evaluated the clinical implications of serum ECP and peripheral blood eosinophil counts as indices of airway inflammation during the follow up of asthmatics (BA). Methods. We repeatedly measured the serum ECP, peripheral blood eosinophil counts and peak expiratory low rate (PFR) during the follow up of 24 symptomatic BA. Results '. Mean serum ECP level of BA at uncontrolled status of airflow limitation was significantly higher than that of controlled state (24.5 +- 3.7 ng/ml vs. 16.2 +- 1.9 ng/ml, p <0.05) and the ECP levels of controlled and uncontrolled status were significantly higher than that of health control subjects (n=10, 10.1+2.0 ng/ml, p<0.01 respectively). Peripheral blood eosinophils were also signifi- cantly increased in uncontrolled status than in controlled status of BA (535.7+81.0/uL vs. 300.4+33.4/pL, p <0.05). In controlled status, 8 BA had higher circulating ECP levels than in uncontrolled status, but with peripheral blood eosinophil counts, only 3 BA had higher levels in controlled status than in uncontrolled status. Variations of PFR correlated with the variations of serum ECP level (r = 0.5370, p<0.01) and variations of peripheral blood eosinophil count (r= 0.6215, p< 0.001). Conelusion.'Measurement of serum ECP and peripheral blood eosinophil count would be useful tools for monitoring the disease activity of asthma, but we could not obtain any more informstions from the measuremert of serum ECP levels than from the peripheral blood eosinophil counts.