Double B perovskite-type series in the system La0.6Ca0.4Mn1-xMexO3-delta with Me=Fe, Co, Ni and x=0-0.6 were synthesized in air by solid state reactions at 1200 degrees C from simple oxides and CaCO3. Almost single phase compositions with small impurities (3-5%) were formed. Replacement of Mn with Me-cations is accompanied by a considerable decrease of electrical conductivity of the prepared ceramics. Lower conductivities of the Me containing compositions compared to La0.6Ca0.4MnO3-delta are explained by stronger polarization of the -Mn(alpha + gamma)+-O alpha--Me(alpha-gamma)+-O alpha--fragments of the -O alpha--Mn alpha+ -O alpha--Mn alpha+ -O alpha--Mn(alpha+gamma)+ -O alpha-Me(alpha-gamma)+-O alpha--chains in comparison with the -O alpha--Mn alpha+-O alpha--Mn alpha+-O alpha-chains without Me-cations, because of different electronegativity of Me and Mn. The double exchange theory gives strong explanation for this phenomenon. Type and level of the electrical conductivity of the La0.6Ca0.4Mn1-xMexO3-delta series are the functions of the [Mn4+/[Mn3+] and [Me3+]/[Me2+] ratios. Mn4+ and Me2+ -cations are possible point defects which determine the p- and n-type conductivity of compositions, respectively. (c) 2008 Elsevier B.V. All rights reserved.