The preparation and topical antiinflammatory potencies of a series of halomethyl 17 alpha-(acyloxy)- 11 beta-hydroxy-3-oxoandrosta-1,4-diene-17 beta-carbothioates, carrying combinations of 6 alpha-fluoro, 9 alpha-fluoro, 16-methyl, and 16-methylene substituents, are described. Key synthetic stages were the preparation of carbothioic acids and their reaction with dihalomethanes. The carbothioic acids were formed from 17 beta-carboxylic acids by initial reaction with dimethylthiocarbamoyl chloride followed by aminolysis of the resulting rearranged mixed anhydride with diethylamine, or by carboxyl activation with 1,1'-carbonyldiimidazole (CDI) or 2-fluoro-N-methylpyridinium tosylate (FMPT) and reaction with hydrogen sulfide, the choice of reagent being governed by the 17 alpha-substituent. Carboxyl activation with FMPT and reaction with sodium hydrogen selenide led to the halomethyl 16-methyleneandrostane-17 beta-carboselenoate analogues. Anti-inflammatory potencies were measured in humans using the vasoconstriction assay and in rats and mice by a modification the Tonelli croton oil ear assay. Best activities were shown by fluoromethyl and chloromethyl carbothioates with a 17 alpha-propionyloxy group. S-Fluoromethyl 6 alpha, 9 alpha-difluoro-11 beta-hydroxy-16 alpha-methyl-3-oxo-17 alpha- (propionyloxy)androsta-1,4-diene-17 beta-carbothioate (fluticasone propionate, FP) was selected for clinical study as it showed high topical antiinflammatory activity but caused little hypothalamic-pituitary-adrenal suppression after topical or oral administration to rodents.