Measurements of electric resistivity, Hall coefficient and mobility as a function of temperature were performed over the temperature range 11-300 K in Cd1-xMgxSe and Zn1-xMgxSe mixed crystals grown by high-pressure Bridgman method. Free electron concentrations of the order of 10(17) cm(-3) can be easily achieved in Cd1-xMgxSe with 0 less than or equal to x less than or equal to 0.4 without any intentional doping. The obtained results show two competing conduction mechanisms; conduction-band conductivity at high temperatures and impurity-band conduction at low temperatures. The low-temperature mobility is influenced by potential barriers due to statistical distribution of charged impurities and fluctuations of composition,