Comments: Here the author does recognize the high cell sterilizing or ‘killing efficiency of alpha radiation in attempting to further his ‘argument that tumor risk is optimized at very low dose, This argument and his additional argument, on the basis of the assumption that the. tumor risk to the tissue subjected to alpha irradiation is proportional to R2t2(t/Te), that "the alpha activity concentration or the activity per particle which is equated to a given tumor risk decreases with increasing time of exposure and also that a given risk can be attributed to smaller cumulative doses when the time of exposure t is appreciably longer than the mean life of the cell, T,", are rather enigmatic with respect to dose and dose-rate relationships with effect, but are subject tothe previous (above) comments on the author's pages 4 and 5. The dose-squared relationship between alpha radiation induced cancer incidence and dose (as in the dog experiments referred to) indicates increasing effectiveness and efficiency of dose in the rising portion of the relationship curve until the curve changes to a plateau before declining at still higher doses, According to this, the rising portion of the downwardly convex curvé shows decreasing efficiency with decreasing dose. Under actual conditions, different amounts of a particular alpha emitter in a particular form and distribution within an organ irradiates cells and tissues for the same time period (t) and with the same decay kinetics, and therefore the dose rate (R) and the dose are determined by the amount of. the alpha emitter taken in or present, The use of the formula R7t7(/T,) with