SQ 26,490, (11 beta, 16 beta)-9-fluoro-1',2',3',4'-tetrahydro-11, 21-dihydroxypregna-1,4-dieno[16,17-b]naphthalene 3,20-dione hydrate (1 : 1), was a moderately potent inhibitor of edema formation in the rat. After extended topical application, SQ 26,490 totally inhibited edema formation without appreciable production of skin atrophy, measured under identical conditions. This atrophy was maintained at a low plateau level of 15-20% at doses beyond those necessary to achieve optimal anti-inflammatory activity. In contrast, the potent corticoids, fluocinolone acetonide and halcinonide, and the moderately potent corticoid, clobetasone butyrate, produced inhibition of edema with a concomitant dose-related atrophy. Hydrocortisone, a weakly potent corticoid, totally inhibited edema and produced at high doses a low atrophy. SQ 26,490 possesses the property for a greater separation of anti-inflammatory and atrophogenic activities than comparative corticoids.