Triamcinolone-induced changes in the number of cartilage cells within the proximal growth plate of the humerus were determined in ICR male mice. It was found that pharmacological doses of corticosteroid hormone possess a direct inhibitory effect upon the proliferative activity of young cartilage cells and thereby adversely affect the growth potential of this growth center. Concomitantly, the activity of chondroclasts also appears to be depressed, thus resulting in a decreased rate of cartilage reorption followed by a slight increase in the number of hypertrophic chondrocytes. It therefore appears that systemic treatment with corticosteroid hormones inhibits the renewal of cartilage cells in the epiphyseal plate, leading to an accelerated ‘aging’ of this growth center with subsequent impairment of long bone gro