Objective: To compare the efficacy and adverse effects of inhaled fluticasone propionate (FP), 400 μg/d, with those of budesonide (BUD), 800 μg/d, in children with moderate to severe asthma. Methods: Three hundred thirty-three children, ages 4 to 12 years, receiving inhaled corticosteroids were enrolled in a double-blind, double-dummy, randomized, parallel-group study. After a 2-week run-in phase, 166 children received FP and 167 received BUD for 20 weeks. The primary outcome variable was mean morning peak expiratory flow; the 2 treatments were to be regarded as equivalent if the 90% CI for the treatment difference was within ± 15 L/min. Pulmonary function, height, and diary cards were assessed at each visit; and morning serum cortisol levels were determined before and after treatment. Results: Baseline peak expiratory flow was similar, FP 236 ± 72 (SD) L/min and BUD 229 ± 74, increasing after treatment to 277 ± 41 and 257 ± 28, a difference between treatments of 12 L/min (90% CI 6-19 L/min; P = .002). Symptom control and use of rescue medication were the same. Cortisol levels after treatment were 199 nmol/L (FP) and 183 nmol/L (BUD) (treatment ratio = 1.09; 90% CI 0.98-1.21; P = .172). Linear growth was less in those receiving BUD (mean difference, 6.2 mm; 95% CI 2.9-9.6; P = .0003). Conclusion: FP at half the dose was superior to BUD in improving peak expiratory flow and comparable in controlling symptoms. Growth was reduced with BUD compared with FP, but there was no difference in serum cortisol suppression or hepatic or renal function. (J Pediatr 1999;134:422-7)