OBJECTIVES--To assess bone and collagen turnover in asthmatic children treated with dry powder budesonide from the Turbuhaler and dry powder beclomethasone dipropionate from the Diskhaler in a dose of 800 micrograms/day. SUBJECTS--Thirteen prepubertal children with asthma. DESIGN--Open crossover study with two treatment periods and treatment free run-in and wash-out periods. All periods were of two weeks' duration. At day 14 in each period blood samples were taken for assessment of serum osteocalcin, the carboxyterminal propeptide of type I collagen (PICP), and the aminoterminal propeptide of type III collagen (PIIINP). At the same time urine was collected for assessment of creatinine corrected pyridinoline (uPYR/cr) and deoxypyridinoline (udPYR/cr) crosslinks. RESULTS--Osteocalcin concentrations were not influenced by any of the treatments. During budesonide treatment mean (SEM) PICP was reduced by 18% (8%) (p = 0.03), PIIINP by 24% (3%) (p = 0.0002), uPYR/cr by 16% (6%) (p = 0.03), and udPYR/cr by 21% (13%) (p = 0.12). During treatment with beclomethasone dipropionate mean (SEM) PICP was reduced by 20% (6%) (p = 0.01), PIIINP by 36% (3%) (p = 0.0002), uPYR/cr by 18% (4%) (p = 0.004), and udPYR by 13% (5%) (p = 0.02). The suppressive effect of beclomethasone dipropionate on PIIINP was more marked than that of budesonide (p = 0.001). CONCLUSION--Treatment with dry powder budesonide and beclomethasone dipropionate 800 micrograms/day is associated with suppression of bone and collagen turnover. The suppression seems to be more marked during treatment with beclomethasone dipropionate. Long term effects and effects of lower doses of budesonide and beclomethasone dipropionate on bone and collagen markers needs further study.