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Olive tree culture is especially important in the Mediterranean area, Spain being first as regards total culture surface (2 121 181ha) and number of productive trees (180 000). Both olive tree culture and olive oil industry produce large amounts of by-products. It has been estimated that pruning produces 25kg of by-products (twigs and leaves) per tree per year. Leaves represent 5% of the weight of olives in oil extraction. On the other hand, the olive oil industry produces 35kg of solid waste (crude olive cake) and 1001 of liquid waste (oil mill wastewaters) per 100 kg of treated olives. Such substantial amounts of by-products may have harmful effects on the environment. Consequently, many alternative utilizations of byproducts have been considered. One important alternative from the quantitative point of view is their utilization as a source of nutrients for animals. Information concerning chemical and nutritional characteristics of the various types of olive tree culture by-products and, particularly, of those by-products resulting from the new industrial procedures applied to olive oil extraction must be generated in order to achieve efficient uses of such by-products in animal feeding. The possibilities of different chemical and biological methods for the nutritive evaluation of olive tree culture and olive oil industry by-products have also to be investigated. Olive tree culture and olive oil industry by-products could play a crucial role as sources of local feeds for small ruminants. They may also contribute to the development of efficient and environmentally conservative extensive animal production systems within Mediterranean semi-arid ecosystems. (C) 1997 Elsevier Science Limited.