The effects of inhaled glucocorticoids on serum markers of bone formation were evaluated in asthmatic children. Serum total alkaline phosphatase (AP), bone alkaline phosphatase (BAP), osteocalcin, and the novel marker of bone formation, carboxypropeptide of type I procollagen (PICP), were measured. In the cross-sectional part, long-term glucocorticoid users were compared with sodium cromoglycate (SCG) users. In the boys (n = 16), but not in the girls (n = 11), PICP was significantly lower in the glucocorticoid users than in the SCG users. PICP correlated positively with BAP (n = 54; groups combined, r = 0.29, p < 0.05). In the longitudinal part, the effects of inhaled budesonide or SCG, both used for the first time, were evaluated before and after 1 and 5 months of treatment. The budesonide dose was 800 micrograms/m2/day for 1 month and thereafter half of that. The SCG dose was 30 mg/day throughout the study. Only during budesonide use did osteocalcin and PICP decrease, the median osteocalcin by 8% at 1 month (p < 0.05) and by 6% at 5 months (n = 15), and PICP by 5% at 1 month (p < 0.05) and by 28% at 5 months (n = 7, p < 0.01). AP and BAP did not change significantly. Decreased PICP suggests decreased bone formation rate. PICP might be clinically useful as a marker of early adverse effects of glucocorticoids on bone.