An experimental investigation of extended-duration operation of lead heat pipes has been conducted. The thermophysical properties of lead were surveyed in the literature, incorporated into the Los Alamos heat pipe design code (HTPIPE), and, in part, confirmed by experiment over a range of temperatures in a Pb/Ta-5wt%W heat pipe. The resulting verified properties were then used in the design of two gas-loaded lead heat pipes, one fabricated from a Mo tube and a Mo-41%Re wick, the other from a Ta-10%W tube and a W wick. The two heat pipes were operated with radio-frequency (rf) induction heating and thermal radiation coupling to the environment. The test configuration was designed to disclose any significant change in wick permeability or pore size (change in capillary limit) by heat pipe dryout during the course of the test. These heat pipes were operated for a period of 4817 hours with no measured change in performance.