A cryostat has been constructed to enable irradiations in a MDS Nordion Gammacell 220 irradiator to be carried out at selected temperatures between 100 and 300K. The principle of operation and the performance of this cryostat are described and results are given of a study into the behaviour of alanine dosimeters at cryogenic temperatures. This work extends previously published data to the region between solid CO 2 and liquid N 2 temperatures and has demonstrated complex dose-dependent behaviour. A sharp discontinuity in the effect of temperature on alanine dosimeter response has been found in the region between 150 and 180K, with no further influence of irradiation temperature on response observed below this point.