We have previously drawn attention to the fact that, in patients suffering from rheumatoid arthritis, the familiar steroid-induced skin-thinning effect which occurs in those given long-term oral corticosteroid medication is absent in those treated with ACTH- (Grahame, 1969). This observation is compatible with the earlier observations of Savage, Copeman, Chapman, Wells, and Treadwell (1962) and West (1961) that 'steroid bruising' is rare in ACTHtreated rheumatoid arthritis patients. This study was undertaken to investigate this apparent disparity of effect between ACTH and oral corticosteroids.It is well established that in vitro corticosteroids (including synthetic analogues) inhibit fibroblast growth and replication (Berliner, Bartley, Kenner, and Jee, 1970). It follows that the 'protective' effect of ACTH could be due to a direct effect of ACTH itself, or perhaps to the effect of androgenic steroids released by the adrenal cortex in response to ACTH stimulation, since it has been shown that the skin of hirsute women is thicker and contains more collagen (Shuster, Black, and Bottoms, 1970) and that their urine contains increased amounts of testosterone (Nabarro, personal communication