The cryogenic and electrical aspects of a program to evaluate superconductors for a dc superconducting power transmission line are presented. Results for conductors in lengths of 20 meters operated at currents up to 10 kA are described. A battery driven power supply which is capable of delivering and controlling currents upto 50 kA is discussed. Specific experiments are discussed which have been designed to probe the response of the conductors to a variety of thermal and electrical conditions, such as: thermal gradients over the length of the conductor, single and two phase flow of cryogen, loss of coolant flow, operation at temperatures near T c , a.c. ripple current, and high current ramping rates.