Alkali metal halides were added to benzoic acid to improve its inhibition efficiency on steel corrosion in 0.5 M H2SO4 medium. 10(-3) M concentrations of NaCl, NaBr and NaI were found to increase the inhibition efficiency of 2.0 x 10(-2) M benzoic acid by 37, 60 and 76%, respectively. Potassium salts of the same anions were less effective, 11, 44 and 65 %, respectively; indicating that sodium ion have a more desirable influence on corrosion than potassium. The decrease in corrosion rate was found to be linear with respect to log of the salt concentration. (C) 2002 Elsevier Science B.V. All rights reserved.