This paper describes a study of the influence of the butyl group as substituent in n-butylamine used as a mild steel corrosion inhibitor in hydrochloric acid solution. An inhibition mechanism is proposed. n-Butylamine, dibutylamine and tributylamine were studied in concentrations from 10(-4) to 1 M and in the temperature range 278-308 K using electrochemical, gravimetric and surface roughness techniques. The three inhibitors adsorbed on the mild steel according to a Frumkin isotherm.