3. 32h. Chinese hamster Chinese hamsters were irradiated whole- or partial-body with 250 kVp x rays [K11]. Judging by the life-span, the upper half of the body appeared more vulnerable than the posterior half and the response to the whole-body ex- posure was largely determined by irradiation of the anterior half. This ob- servation seems quite unique to this species and at variance with data obtained in the mouse [K7, B8, C25] and in the rat [D7, L17]. A significant increase of the incidence of tumours in irradiated animals was ascertained only of the ovary. Progressive capillary glomerulosclerosis was observed as in all animals examined and this lesion was accelerated by irradiation. C. 325. CONCLUSIONS It appears, in conclusion, that keeping the animals under environmental temperature conditions which are thought to be suboptimal may decrease, rather than enhance, the life-shortening effect of a radiation treatment. Also, stress of a rather non-specific nature (cold, starvation, water deprivation, physical exercise, electric shock) may have some influence on the life-span of the ir- radiated animals, owing presumably to some interaction between the effects of stress and of radiation exposure. These unconventional data are, however, too few, the treatments tested too unspecific and their underlying mechanisms too obseure to warrant undue generalization. Hypoxia induced by various techniques induces invariably some protection against the life-shortening action or ra- diation, but the extent of this protection is probably less than that produced by the same treatments against acute radiation effects. 326. Treatment shortly before irradiation with a number of radioprotective chemicals (MEA, AET, 5 - HT, cysteamine, PAPP and others) affords a certain amount of reduction of the life-shortening effect, by comparison with irradiated untreated controls. The nature and the dose of the drug; the dose of radiation in relation to the form of the relationship and to its possible mo- dification by the drug treatment; the strain and sex of the animals; are all variables that may to some extent modify the final outcome of the drug-radiation interaction. The effect on longevity of these drugs is often smaller, sometimes marginal, by comparison with the effect produced by the same drug treatments on early mortality: dose reduction factors in the region of 1.4 to