The inhibitive action of two isomers of bipyrazolic type, namely, 4-{bis[(1,5-dimethyl-1H-pyrazolyl-3-yl)methyl]amino}-phenol (isomer 1) and 4-{bis[(3,5-dimethyl-1H-pyrazolyl-1-yl)methyl]-amino}phenol (isomer 2), against the corrosion of steel in I M hydrochloric acid solution has been investigated at 308 K using weight loss measurements, polarisation and impedance spectroscopy methods. The inhibition efficiencies evaluated from the methods used are in good agreement. The polarisation curves reveal that these bipyrazolic compounds act as mixed-type inhibitors. These studies show that these compounds are efficient inhibitors. Inhibition efficiencies reach about 95 % for isomer 1 and 2 at 5 x 10(-4) M. The temperature effect on the corrosion behaviour of steel in 1 M HCl with and without the bipyrazolic compounds is studied in the temperature range from 308 to 353 K at 5 x 10(-4) M. The activation energy for steel corrosion is determined. The isomers adsorb on the steel surface according to a Temkin isotherm adsorption model. (C) 2004 Elsevier B.V. All rights reserved.