1. Study of uptake and retention. The PROPOSAL, while not entirely in accord with epidemiologic methodology, standard is I think well adjusted to the actual conditions in which the field work must be done. I favor building upon the plan. would recommend, complete, Hence The principal addition I as a preliminary, is the development of a stratified sampling frame before field work starts. This sampling frame, or list, of the affected population will systematize all existing information about such factors as age, sex, exposure. location of occupation and potential One advantage in this particular case is that this listing can make full (ground area survey, mination, residence, together use of the other elements of study animal sampling and particle-size deter- with the earlier work in these three areas). The function of such a sampling frame is to provide the necessary basis for design and implementation of an optimal stratified random sample for accurate determination of uptake and retention. The intent is to follow the main outline of the PROPOSAL requiring annual measurement of levels in small samples of approximately six subgroups of the population: once the frame is complete, any statistician on our collabo- rator's staff could design this sample readily. samples would not turn out exactly 10, while still satisfying objectives. Subgroup but can be kept small The most difficult element here is sampling randomly in the field: but this is worth insisting upon because of the scientific value of determinations made in this way. QS 53009 830