A simple, sensitive pulse shape discriminator is described, which was designed to permit detection of low energy neutrons in the presence of a very high &ggr;‐ray background, and at high counting rates. An improvement relative to discrimination circuits published so far was obtained by incorporating a fast crystal diode switch for the separation of the fast and slow parts of the scintillator de‐excitation pulse. This device greatly reduces interference effects of nearly coincident detector pulses and also permits better pulse matching and comparison. The best discrimination was obtained for moderate sensitivity and counting rates, where out of 105detected &ggr; rays about one was erroneously admitted. A detailed description of the circuit and accessories is given, and results of test runs at a 20 Mev FM cyclotron are presented.