The low interference with growth expected in child for a cortisol analogue, deflazacort (DFZ), prompted us to verify if DFZ could affect growth less than prednisone (PDN). An interim analysis relative to 27 girls and 38 boys (out of 100 expected) aged 3-12 yrs, after a median period of 14 mo.s is reported. Children with connective tissues (CTD) and glomerular disorders (KD) were randomly allocated to DFZ or PDN. Anthropometric measurements and maturity ratings were performed. Mean daily doses of PDN (or DFZ equivalent), from 0.57 to 0.64 mg/kg (DFZ 0.92 to 0.94 mg/kg) to induce control and from 0.19 to 0.39 mg/kg (DFZ 0.34 to 0.36 mg/kg) to maintain disease under control were given in CTD and KD, respectively. The increase in bone age delay over time was significantly greater than for PDN (-4.0 mo/yr) than DFZ (-1.8 mo/yr) in the overall group. The increases in statural age delay and loss over time were significantly greater than for PDN (-5.9 and -5.9 mo/yr) than DFZ (-2.4 and -2.4 mo/yr), only in children with "taller" midparents. Although doses of DFZ 1.1-1.8 times those of PDN were given, growth retardation in PDN-treated children was nevertheless 2.3-2.5 times that in DFZ-ones.