Recently, Gamal et al. [phys. stat. sol. (a) 191, 322 (2002)] reported the results of electrical conductivity, Hall effect and thermoelectric power (TEP) measurements on Tl5Te3 single crystals. The samples used in the study were p-type semiconductors. From the experimental data for the temperature dependence of TEP, Gamal et al. determined the values of 1.6 x 10(-41) kg and 1.5 x 10(-40) kg, respectively, for the effective masses of electrons and holes in p-type Tl5Te3, which are about ten orders of magnitude smaller than the free electron mass, 9.11 x 10(-31) kg. We argue that the anomalously small values obtained for the effective mass of charge carriers in Tl5Te3 have no physical significance. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.