This paper presents the results of performance tests of several dual-slot heat pipe test articles. The dual-slot configuration has a very high thermal transport capability and has been identified as a very promising candidate for the radiator system for the National Aeronautics and Space Administration (NASA) Space Station solar dynamic power modules. Two six-foot long aluminum heat pipes were built and tested with ammonia and acetone. A 20-ft long heat pipe was also built and tested with ammonia. The test results have been compared with performance predictions. A thermal transport capacity of 2000 W at an adverse tilt of one inch and a 1000 W capacity at an adverse tilt of two inches were achieved on the 20-ft long heat pipe. These values are in close agreement with the predicted performance limits. This work was performed by Grumman as part of the work under Contract NAS3-24665 for NASA-Lewis Research Center.