The Pacific Intertie has the world's longest highvoltage direct current (HVDC) transmission line. Its presence in proximity to communications circuits poses a potential interference problem with respect to electrostatic and electromagnetic induction and a possible electrolysis problem with respect to underground metallic structures located near the line's earth electrodes. This paper traces the history of testing endeavors by representatives of interested and concerned agencies, companies, and utilities in an attempt to define the magnitude of the problem in order that mitigative measures could be planned.