The throughput of a local slotted ALOHA radio network using PSK modulation over Rayleigh fading channels is analysed. The capture effect is related to the modulation technique, signal/noise ratio of the received signal, distribution of terminals in the area and the length of the transmitted packets. Owing to the capture effect a maximum throughput of 0.75, rather than 0.36 with no capture, is predicted. This improved performance is observed in the slow fading channels with a very high signal/noise ratio.<<ETX>>