A reliable laboratory assay for rapidly quantitating the topical anti-inflammatory efficacy of steroids has been established. Croton oil, applied topically to the rat ear, elicited an acute phlogistic response which could be quantitated by removal and weighing of the ear 6 hr later. Co-application of increasing concentrations of corticoids resulted in grossly related decreases of the phlogistic responses; removal of thymi 48 hr subsequent to application permitted assessment of systemic action. The topical antiphlogistic effects of hydrocortisone, cortisone, corticosterone, prednisolone, 6a-methylprednisolone and triamcinolone grossly paralleled their thymolytic activities. Utilizing the topical assay methodology, 9a,ll(8-dichloro-21-hydroxy-16a,17a!-(isopropylidenedioxy)-l,4-pregnadiene-3,20-dione exhibited an antiphlogistic potency of 23.2 relative to hydrocortisone, while the relative thymolytic potency was less than 1.0/ {Endocrinology 11: 625, 1965)

Reports from several laboratories have established the existence in extracts of hu-

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Each group contains 6 9 rats.t The standard deviations for various groups and times ranged between k 1 6 and k 2 4 .

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