ABSTRACT: Collagen production by human skin fibroblast cultures was studied by incubation with [3H] proline and several glucocorticosteroids known to produce dermal atrophy in vivo. Collagen production was measured as formation of [3H]hydroxyproline or collagenase-digestible3H-polypeptides, and the values were corrected for changes in cell number in the same cultures. The steroids, in a wide concentration range, failed to elicit any consistent alterations in collagen production. Review of the literature dealing with corticosteroid-induced changes in collagen production by human skin fibroblasts indicate conflicting results even under apparently similar incubation conditions. Consequently, no unifying hypothesis for steroid-induced dermal atrophy can be developed presently based on the in vitro data.