A comparison has been made between two programs intended for the performance analysis of a horizontal-axis wind turbine. One program, WIND14, is based on the blade element / momentum theory of propellers, while the other, VORTEX, uses helical vortex theory. The programs differ also in terms of input/output versatility, airfoil aerodynamic modeling, and in the amount of execution time and number of calculations required for a given result. Two basic types of comparison are offered: In the first case, the programs employ identical basic airfoil data, so as to isolate, to as great an extent as possible, the differences arising directly from the applications of the two theories. In the second case, each program was allowed its greatest versatility in attempting to predict the electrical output of the Boeing Mod-2 Wind Turbine System, for which extensive empirical data is available. The results indicate that, in general, the vortex code will pred ict lower cut-in windspeeds and lower peak power than will WIND14, given identical airfoil data, while the system power predictions of both programs fall within the scatter of the available Mod-2 empirical data for the range of windspeeds between cut-in and rated power. To produce a given result, VORTEX requires approximately 15 times as much CPU time as does WIND14, although storage requirements are approximately the same.