Comments: It is not at all obvious what "these reasons" are, nor what they do or are supposed to support. If the "reasons" are what immediately precedes the statement, there is little upon which to base a judgment other than the assumptions upon which the author bases his speculations, If the "reasons" are the preceding 17 pages, these have been discussed in detail previously. Page 18, lines 5-7 - "Similarly plutonium-239 in mixed fallout particles may be expected to produce more tumors per disintegration than is the case for pure 38pu02 and 239Pu05." Comments: That this "may be expected to produce more tumors per disintegration" depends upon the validity of the assumptions of the author. Page 18, lines 7-il - "However although larger burdens of hot particles will be required for a given tumor risk, such risks can be expected to increase with both alpha specific activity and with particle surface area, and the effects should occur earlier for a given burden of smaller particles of higher specific activity." Comments: This sentence is very enigmatic, starting with "a given tumor risk" which is subsequently variable, ending with "a given burden" which earlier was larger (larger than what is not stated), and meanwhile varying specific activity, surface area and time. Nor is it clear that it is consistent with the two preceding sentences and earlier statements regarding the relative risk of high specific activity versus low specific activity particles. Page 18, lines 12-15 - "The above considerations make it obvious that the present practice of averaging the alpha dose over the whole lung or some arbitrary fraction thereof 10-13) and grossly misleading procedure at best." is a highly questionable