Inhaled steroids are frequently used in childhood asthma, but concerns based on limited objective evidence remain, regarding long-term side-effects. In this study the systemic effects of standard doses of inhaled steroids in childhood asthma were assessed, comparing beclomethasone dipropionate (BDP) with fluticasone propionate (FP). The study was prospective, randomized and double-blind. Twenty-three steroid-naive children with moderately severe asthma, aged 5-10 yrs, were allocated either BDP (400 microg x day(-1) or FP (200 microg x day(-1)) using a metered-dose inhaler with a spacer. Asthma control was assessed at regular intervals over 20 months. Fasting morning blood and overnight urine samples were collected for estimation of serum cortisol, serum 1-carboxyterminal telopeptide (ICTP), serum osteocalcin and urine deoxypyridinoline (DPD). Bone mineral density (BMD) was measured at each visit. None of the markers of bone turnover showed any change during the study period. BMD increased at normal rates with age. Serum cortisol significantly decreased on BDP, but not on FP. A significant difference in growth rates was found between the groups, with a slower rate of growth towards the end of the observation period in the BDP group. In conclusion when taken in a relatively modest dose over a period of time, beclomethasone dipropionate had significant effects on the hypothalamic-pituitary-adrenal axis and statural growth in childhood asthma. These systemic effects were not seen with an equipotent dose of fluticasone propionate.