A new procedure has been proposed for the photometric determination of arsenic as its compounds with tetrazolium salts. The choice of 5(1,3-benzadioxole-5-yl)-2-(4-iodophenyl)-3-phenyl-2H-tetrazolium chloride as a reagent for arsenic has been substantiated. The developed scenario of sample preparation involves the gas extraction of arsenic as arsine from the reaction mixture and its absorption isolation from the gas phase into a reagent solution in a 10:3:12 water-butanol-1-dimethyl sulfoxide mixture. The procedure provides the determination of from 1 to 120 μg/L arsenic.