The influence of 1-phenyl-2-aryl-5,6-dihydroimidazo[2,1-b]thiazolium bromides on the corrosion-electrochemical behavior of St.20 steel in acid medium (0.1 M HCl) was studied. Variation of the partial coefficients of inhibition as a function of polar properties of substituents in the benzene ring of the inhibitor was discussed. © 1996 MAEe cyrillic signΚ Hayκa/Interperiodica Publishing.