There has been increasing interest in modeling arc welding processes and other metallurgical processes involving plasmas. In many cases@ the published properties of pure argon or helium gases are used in calculations of transport phenomena in the arc. Since a welding arc contains significant quantities of metal vapor@ and this vapor has a considerably lower ionization potential than the inert gases@ the assumption of pure inert gas properties may lead to considerable error. A simple method for calculating the electrical and thermal conductivities of multicomponent plasmas is presented in this Bulletin. Publication of this report - WRC Bulletin No. 357 was sponsored by the Welding Research Council. A simplified road map of the plasma physics literature for calculation of electrical and thermal conductivities of metallurgical plasmas is presented. The presence of even small quantities of metal vapors in argon or helium plasmas can greatly influence these conductivities. Although very complex computational procedures have been developed by theoretical physicists@ in most cases@ simplified formulas provide estimates of plasma properties which are well within the limits of error in the physical measurements of these systems.