Values of ambient solar ultraviolet radiation and estimated hourly radiation for both erythemal (UVB) and UVA radiation are presented for the latitudes where the major studies of human cutaneous melanoma have been performed; 50-55 degrees N (Denmark and Western Canada), 30-34 degrees S (Western Australia) and 15-27 degrees N (Queensland). Comparisons are made for exposure patterns relating to constant and to intermittent exposure, and combinations of these. The results show that the wavelength distribution of solar ultraviolet radiation varies with latitude and exposure pattern. At higher latitudes, the contribution of exposure at peak periods is more marked. The comparison or combination or results from epidemiological studies at different locations will be aided by this consideration of the variation in different aspects of solar radiation, and tables are given for this purpose.