The environmental factors including geography, geology and soil have been reviewed in areas of high prevalence of non-filariasis endemic elephantiasis surveyed in tropical Africa. These areas occur at altitudes above 1000 m where rainfall is seasonal and exceeds 1000 mm annually. The soil is a red clay, very slippery when wet and very adhesive if allowed to dry on the skin. These are also areas of past or present alkalic volcanism, the prevalence being highest in proximity to the volcanoes. The derived soils are notable for the high proportion of alumino-silicate particles of colloid size in the clays. The significance of these findings suggests that the number and small size of the clays. The significance of these findings suggests that the number and small size of the particles facilitates entry through the skin into the lymphatic tissues, where they exert the known irritant and fibrosing effects of silica and alumina.