The extension of soybean cultivation in the south part of Europe is limited by climatic conditions and, above all, by drought appearing each year during summer, in a time which is a critical period for water supply of soybeans: the grain and pod filling stages (Mingeau , 1975). By action of this drought, grain yields may decrease drastically. As irrigation is often impossible, one of the most important breeding objectives in France is drought tolerance . Although water relations of ten should be studied in soybeans , varietal differences were rarely investigated except by Mederski and Jeffers (1973) and Sammons et al. (1978 , 1979).