mice. Life-span-shortening, incidence of thymic or myeloid leukaemia, and the occurrence of tumours of breast, ovary, lung and uterus were the end-points evaluated. Dose reduction factors of 1.7 for APT and 1.4 for 5 - HT could be calculated for long-term survival, which values were close to those obtained for short-term survival. For the induction of all tumours the respective dose- reduction factors were 1.5 and 1.4; for the induction of thymic lymphoma 1.8 and 1.6. C. 1. 311. BIOLOGICAL TREATMENTS Bone marrow transplantation Syngeneic marrow transplantation was not very effective in protecting against reduction of longevity in Cosgrove's et al. [C23] experiments. This treatment did inhibit the induction of thymic lymphoma, in accordance with other data [C13, K16, 112, C2h] but did not alter the incidence of glomerulosclerosis, solid tumour induction (ovary, breast, lung, uterus) or lens opacities. 312. Experiments on the late somatic effects in syngeneic radiation chimaeras were performed by Covelli et al. [C13] on (C57BLxC3H)F1 male mice. Bone marrow treatment was effective in increasing survival of the animals within 60 days, but the mean and median after-survival of the mice irradiated with 900 rad of x rays were not influenced by the number of cells injected (in the range of 8 10! - 1 10! cells/mouse). Irradiation with 900 rad of 250 kVp x rays fol- lowed by bone marrow treatment was very effective in decreasing the occurrence of reticulum cell sarcoma in long-term survivors but led to an enhancement of tumour incidenc (particularly in the malignant tumours) by comparison with untreated animals. Irradiated bone-marrow-treated animals had a greatly enhanced and accelerated appearance of nephrosclerosis which was by far the most important cause of death between 600 and 700 days of treatment under these conditions. e. 313. Other treatments In order to investigate on the frequently reported finding of a greater sensitivity of the female animals of life-shortening (see paragraphs 246-254) Holland et al. [H13] investigated the effect of ovariectomy on RFM mice. Castration had little effect on overall mortality rate, both alone or in com-