-2in former smokers and in irradiated humans indicates, contrary to Dr. Martell's suggestion, that the etiology is different in the groups. Uranium miners who have stopped smoking do not show this pattern of declining risk typical of unirradiated populations; about 30% of the cancer deaths in uranium miners have occurred in former smokers even though more than half of them had not smoked for five years or more. This suggests that the effects of the smoke as a whole, or apart from the contained alpha emitters, are probably much more important than the permanent effects of the small amounts of alpha emitters in the smoke, in regard to the mechanism of induction of the associated lung cancer. While Dr. Martell provides evidence regarding the presence of very small quantities of alpha emitting radionuclides in definitive structures of the tobacco leaf, his conclusions go considerably beyond the data provided, Page 2, lines 28-29 - "And for long term exposures, unacceptably high tumor risks appear to be associated with picocurie burdens of internal alpha emitters." Comments: If this conclusion is based upon the tobacco smoking statistics, the previous response is applicable here also. also Page 3, lines 1-5 - "It/is possible that the critical health effects for alpha emitting particles are the incidence of atherosclerosis and other degenerative diseases of the cardiovascular system. The published evidence supporting these conclusions is briefly reviewed below." Comments: The evidence which the author presents in support of his conclusions is reviewed below. Page 4, lines 13-16 - "The alpha radiation-induced bone tumor incidence in dogs is observed to be proportional to the square of the alpha dose 1 implying that a sequence of two or more low probability events must be involved."