Propanol, propanediol and propanetriol (glycerol) have been extensively investigated in the past by means of dielectric spectroscopy, studying both pure and in mixtures with non-polar or polar solvents, and in other cases in aqueous solutions. In view of the lack of a complete model that explain satisfactorily the dielectric behaviour of this substances, valuable information can be obtained from comparative studies, because they have the same chain length and the differences must be due to the increasing number of dipoles of each molecule. In this Letter, the values obtained for permittivity as function of temperature are compared, as well as the fittings of the three substances in the pure state, with a modification of the Onsager equation. One of the parameters of the fittings follows the trend observed for the alcohols and the other tends to the values of permittivity at very high frequencies given in the literature. A good agreement is obtained between the experimental values and the fittings, showing this fact that polyalcohols behave, under this point of view, like the mono-alcohol. (C) 2004 Elsevier B.V. All rights reserved.