This study attempts to estimate the effect of a drought stress on the growth of vegetative parts and on the yield components in soybeans. In the same time the genetic variability for drought resistance has been observed. Fifteen varieties were cultivated in drought boxes (1 m x 1 m x 0,5 m, 36 plants per box) and, since flowering time until maturity, two water treatments were applied : in the first one, the needs of the plants were filled and, in the second one, water supply was exactly the half of the first. Every two weeks after the beginning of flowering, five plants were harvested in each variety and each water treatment : measurements of the main canopy and stem morphological traits were made. At maturity, thirty plants were harvested in each variety and each water treatment and the principal yield components were measured. The leaf area index and the water contents of leaves, petioles and stem were the parameters affected the most rapidly by the drought stress. For the yield components, the number of pods per plant was the most sensible character. A drought resistance index was calculated for each variety, based on the ratio between the grain yield in each water treatment. The validity of the experimental procedure and of the drought resistance index is discussed. Results show large differences in varietal responses to the drought stress. So it seems possible to improve by a breeding program the drought resistance of soybeans.