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The comparative magnitudes of the differences in the skin reflectances between various populations are dependent upon the wavelength at which reflectance is measured.The relationships between mean reflectances of several populations measured at wavelengths 425 mμ and 685 mμ and between wavelengths 550 mμ and 685 mμ show a curve, when represented in a graph.The corresponding relationships between reflectances of individuals within a population do not show a curved pattern because of the relatively small variability of the reflectances. However, the main orientation between reflectances measured at wavelengths 425 mμ and 685 mμ in the intra- populational distributions agrees with that of the interpopulational curve.“Tanning capacity” (Red/Green ratio) derived from forehead and upper arm readings has the same value as that calculated from pre- and postirradiation readings at one site.The analysis of the significance of several factors known to influence skin reflectances does not result in a clear insight into the background of the relationships between reflectances of light at different wavelengths. Factors inherent to the measuring method may play a major role.