RECENTLY it has been suggested1–3 that electron spin resonance studies of irradiated amino-acids reveal thermal effects as well as directly induced free radicals. The model proposed is that absorption of radiation energy may lead to a localized heating of small regions; this may allow radical reactions to take place at a rate characteristic of a much higher temperature than the average temperature of the sample. Evidence for this model includes the fact that there are differences in the spectra from irradiated glycine and valine after very high doses and lower doses of radiation energy1; the effects of different linear energy transfer radiations2; and the changes in the glycine spectra as functions of dose and time3. The validity of such a model depends on the assumption that the energy deposited by the radiation cannot diffuse by a conduction process, as only then can a local “hot spot” be created. A theoretical examination of this problem is hampered, however, by a lack of knowledge of the processes involved; in particular, no measuremeDts have been made, as far as is known, on thermal conductivities. As a first step, an investigation was therefore made of the thermal conductivity of a single crystal of glycine.