Serum concentrations of growth hormone-dependent insulin-like growth factor I (IGF-I) and insulin-like growth factor binding protein-3 (IGFBP-3), the carboxy terminal propeptide of type I procollagen (PICP), the carboxy terminal pyridinoline cross-linked telopeptide of type I collagen (ICTP) and the amino terminal propeptide of type III procollagen (PIIINP) were studied in 14 prepubertal children with asthma (mean age 9.7 years) during treatment with inhaled budesonide. The study design was a randomized, crossover trial with two double-blind treatment periods (200 and 800 micrograms) and one open, non-randomized treatment period (400 micrograms). All periods were 18 days' duration. Budesonide treatment was associated with a dose-related suppressive trend in serum concentrations of PIIINP when the 400 micrograms period was included (p <0.01; z = -2.7) and when it was excluded from the calculations (p <0.01; z = -2.6), indicating reduced synthesis of type III collagen. A similar trend was observed in ICTP levels when the 400 micrograms period was excluded from the calculations (p = 0.05; z = -1.9). No other statistically significant variations were seen.