The inhibiting action of a nonionic surfactant of the TRITON-X series (TRITON-X-405) on stainless steel type X4Cr13 in 1.0 M H2SO4 solution within the temperature range of 25-45 degrees C was studied using the gravimetric and potentiodynamic technique. The inhibition efficiency was found to increase with the inhibitor concentration and decrease with temperature. The satisfactory inhibition efficiency of TRITON-X-405 on SS type X4Cr13 in 1.0 M H2SO4 was limited to temperatures below 35 degrees C or at the surfactant concentration higher than c = 10(-5) M. The adsorption of TRITON-X-405 on stainless steel type X4Cr13 in one molar of sulphuric acid within the chosen temperature range follows the Flory-Huggins adsorption model with very high negative values of the free energy of adsorption Delta G(ads). The thermodynamic parameters, such as the heat of adsorption and adsorption entropy, were calculated by employing thermodynamic equations. Activation parameters such as apparent activation energy, activation enthalpy, and activation entropy were evaluated from the effect of temperature on corrosion and inhibition processes. Those entire apparent activation parameters show an increase-decrease characteristic (a nonmonotonic function). They increased at concentrations lower than the cmc of added surfactant and decreased when the concentration of TRITON-X-405 was higher than c = 10(-5) M.