N-type conduction was observed in epitaxial Pb1-xSnxSe and Pb1-xSnxTe thin films grown by MBE with an increasing charge carrier concentration as well as an increasing thermopower value related to an increasing tin content reaching up to 12at%. The lattice thermal conductivity decreases as expected due to alloy scattering but the carrier mobility is almost stable. All these effects increase strongly the thermoelectric properties of Pb1-xSnxSe and Pb1-xSnxTe. The n-type conduction arises from a metal excess in the stoichiometry range. The same type of conduction has also been found in bulk samples. Bulk single crystals of Pb1-xSnxSe and Pb1-xSnxTe are grown by the unseeded vapor growth technique. A rather constant mobility and a decreasing thermal conductivity with increasing tin content are measured in the n-type bulk samples. A figure of merit of ZT=0.9 was measured at 325°C for a Pb0,965Sn0,035Se sample with a carrier concentration of about 9.3E18 cm-3, i.e. already better than known n-type PbTe-based materials for this temperature range.