o-Methyl-p-methoxyphenyldithiophosphonic acid (MTPA), o-ethyl-p-methoxyphenyl-dithiophosphonic acid (ETPA) and o-isopropyl-p-methoxy phenyl dithiophosphonic acid (IPTPA) ammonium salts were used as inhibitors on steel corrosion in 1 M HCl medium. Concentration of the inhibitors were in the used-as inhibitors on steel corrosion in I M HCl medium. Concentrations of the inhibitors were in the range 10(-3) to 2 x 10(-2) M, five different temperatures between 298 and 338 K were tried; Tafel extrapolation and linear polarisation techniques were employed. Corrosion parameters and adsorption isotherms were determined from current-potential curves. At room temperature, the three compounds were found to decrease the corrosion rate by around 80% at 1 x 10(-3) M, and 95% at 2 x 10(-2) M concentration. The inhibition efficiencies weaken slightly at higher concentrations but in any case, more than 75% inhibition is observed at a temperature of 338 K with an inhibitor concentration of 2 x 10(-2) M. Surface coverage degrees indicate that the adsorption pattern is consistent with the Temkin isotherm. © 2005 Elsevier B.V. All rights reserved.