SUMMARY.-On the basis of data gathered from long term residents of 3 widely separated regions of Queensland a multivariate analysis has been made to determine the influence of a number of factors in the aetiology of skin cancer and solar keratosis. Factors considered were age, sex, susceptibility to sunburn, complexion, eye colour, ancestry, occupation, clothing habits and residential district. For both sexes, both diseases and all age groups the factor " susceptibility to sunburn " proved to be the most powerful single discriminant. On the whole it appeared that the genetically based factors as a group provided more information on susceptibility than the environmental factors. The relative importance of " occupation " remains in some doubt. In the tropical area away from the coast it appears to be of considerable importance. In coastal areas its influence appears to be blunted, presumably by factors such as sports and recreation habits.AN earlier article in this series (Carmichael and Silverstone, 1961) used actuarial techniques to estimate the cumulative lifetime risk of incurring skin cancer in various parts of the coastal areas of Queensland, Australia. The proportion of males between 20 and 80 years of age who might be expected to produce at least one cancer varied from about 5 or 60 in the sub-tropical areas around Brisbane, to 12 or 130% in the tropical areas of Townsville and Cairns some 1000 miles nearer the equator (see Fig. 1). Rates for females were about 50 to 60% of those for males.These estimates were based on recorded data at the various skin cancer clinics, and while the survey would have provided reasonably accurate results it was not possible to relate the prevalence of skin cancer to the personal characteristics of those affected. The existence of such extremely high risks makes it possible, however, to conduct field surveys of the population to achieve this latter purpose. With this in view, three separate field surveys were made in areas which had widely different climatological conditions but which at the same time provided a good cross-section of the population.Procedures have been described in detail in two preliminary reports (Silverstone et al., 1963;Silverstone and Gordon, 1966) but for convenience a brief summary follows.Regional Surveys The areas studied were located on the sub-tropical coast (annual sunshine 2740 hours; annual rainfall 44 inches); the dry north-west tropical inland (sunshine 3300 hours; rainfall 17 inches); and the wet north tropical coast (sunshine 2660

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