The inhibition of the corrosion of mild steel in I M HCl by 3,5-di(m-tolyl)-4-amino-1,2,4-triazole (m-DTHT) and 3,5-di(m-tolyl)-4H-1,2,4-triazole (m-DTHT) has been investigated at 30 degreesC using electrochemical and weight loss measurements. Polarisation curves reveal that m-DTHT is a mixed type inhibitor whereas m-DTAT is a cathodic type inhibitor. Inhibition efficiencies up to 95% for m-DTAT and 91% for m-DTHT can be obtained. Adsorption of these inhibitors on the mild steel surface is found to obey the Langmuir adsorption isotherm. The effect of temperature on the corrosion behaviour with addition of 4 x 10(-4) M of m-DTAT and m-DTHT added was studied in the temperature range 30-60 degreesC. The associated activation corrosion and free adsorption energies have been determined. The comparative study of triazole derivatives indicates that the corrosion inhibition efficiency of the aminotriazole is greater than that of the 4H-triazole. (C) 2002 Elsevier Science B.V. All rights reserved.