- 27 - at low dose rates. By ccntrast, structural changes resulting from alpha interactions are directly proportional to the number of inter- ‘actions and are independent of alpha interaction rates," The proper interpretation or expression of the content of the quoted statement under comment and the quoted statements in the comments, is that for alpha radiation the incidence of induced chromosomal structural changes increases linearly (proportionally) with increasing dose, and also with dose rate under realistic conditions for internal alpha emitters where dose rate and dose are dependent upon amounts of alpha emitter present. On this linear relationship basis the effective- ness of the alpha radiation per unit dose (efficiency) is independent of dose rate, as contrasted with the dose-squared dose-effect relationship for x- or y-rays and the dependence of effectiveness and efficiency on dose size and dose rate. However, it should be pointed out that either the linear or the dose-squared dose-effect relationship pertains only to the point of saturation of effect, with no further increase in the specified effect with further increase in dose. Furthermore, at very low doses of alpha radiation, if there were any reduction in efficiency of production of any particular type of chromosomal effect or other effect, which could be possible, this would indicate the possibility of an effect-reducing influence of reduced dose-rate, Page 13, lines 19-22 - "However, the cumulative effects of internal alpha emitters gives rise to an increase in the populations of mutated cells (cells with viable structural changes in their chromosomes) and in the health consequences of such changes." Comments: This is true insofar as it means that the increasing dose with