Corticosteroids are being used to prevent or ameliorate respiratory distress syndrome. An evaluation of possible deleterious effects was undertaken in Caeserian-derived Sprague-Dawley rats by giving 1.25mg of cortisone acetate I.M. on the 4th day of life to 20 pups; 25 controls received 0.05ml saline. This dose is equivalent to approximately 70 mg/M2 of prednisone. Pups were reared in litters of 8 (all treated or all control); terramycin was added to the drinking water. At age 21 days body weight, stem-length and tibia length were all less in the cortisone treated animals than the same measurements in the controls, but skeletal maturation was advanced in the treated animals.At age 12 weeks, decreased body weight (male p 0.01<>0.001;female p 0.02<>.01) and bone length (male p 0.10<>.05; female p 0.05<>0.02) were still evident but the number of eplphyseal fusions was the same in treated and control animals. These findings have implications for the future growth of infants given corticosteroids because reduced linear growth and accelerated skeletal maturation will eventuate in short stature.