Pyrazole carboxylic acid derivatives of 5-amino-1,3,4-thiadiazole-2-sulfonamide (inhibitor 1) were synthesized from ethyl 3-(chlorocarbonyl)-1-(3-nitrophenyl)-5-phenyl-1H-pyrazole-4-carboxylate compound. The inhibitory effects of inhibitor 1, acetazolamide (AAZ) and of 11 newly synthesized amides (5a-b, 6, 7a-g, and 8) on hydratase and esterase activities of carbonic anhydrase isoenzymes (hCA-I and hCA-II) have been studied in vitro. The comparison of newly synthesized amides to inhibitor 1 and to AAZ indicated that the new derivatives inhibit CA isoenzymes and they are more potent inhibitors than the parent inhibitor 1 and AAZ. (C) 2010 Elsevier Masson SAS. All rights reserved.