The use of threshold detector foils to measure the external neutron spectrum of two reactors is described. The foils employed are Pu236 to measure the total fast flux, U238 for the region above 1.5 Mev, S32 above 2.5 Mev, and Au197 for thermal neutrons. Scintillation counters ae used to determine the activity induce din the detectors. The foil-counting system is calibrated by used a Cockcroft-Walton accelerator as a fast neutron source. The results indicate a fission type spectrum at each reactor.