Model for the global irradiance of the solar biologically-effective ultraviolet-radiation on inclined surfaces. The body surface area of man is the relevant receiving surface for solar UV radiation. To consider this body surface geometry, the biologically-effective UV radiation of the solar global radiation was measured. This was done at 26 differently aligned measuring points whose orientation was determined by the angle of inclination (vertical) and the azimuth (horizontal). Approximately eight hundred sets of measurement series were carried out at 33 different sites. A simple model, developed from the data obtained, made it possible to calculate relative irradiance as a function of the angle of inclination and the ground reflection (UV albedo). Thus relative risk of solar UV exposure to different regions of the body can be assessed. In addition to this, if the irradiance on a horizontal plane (measured or calculated by a corresponding model) is taken into consideration, the absolute values for UV irradiance on tilted planes can be determined. Published in Photochemistry and photobiology (1990)