In spite of the fact that cowpea (Vigna unguiculata (L.) Walp.) is one of the most drought-tolerant crops, its production in dry Sahel environment is affected by very intense water deficit that usually occur in the course its growth cycle. The objective of this work was to compare with the help of agromophorlogical criteria, the degree of sensitivity to water deficit of the early maturing, erect cowpea varieties and the late maturing, semi-erected or crawling varieties. The effect of severe water deficit applied at the vegetative phase until the beginning of floral initiation was studied during the dry season in 1999 at Bambey (Senegal). The agronomical observations were focused on the soil water status, the dynamism of vegetative development and root growth, yield and yield components. The sensitivity of the varieties to water stress were assessed by water stress index (ls) and water use efficiency (WUE) for the pods, grains and the total biomass productions, respectively. The results obtained showed that the early maturing, erect varieties were more sensitivity to drought than the other varieties. This sensitivity was deduced from very high Is for the grains (0.61), the pods (0.54) and a lower WUE for grain production (3.27 kg ha-1 mm-1) under water stress as against 6.41 kg ha-1 mm-1 under optimal water conditions. It was observed that under water deficit at pre-floral phase at the three varieties, an increase in the mean grain weight correlated with the reduction in grain number per m2. At the plant population level, the results obtained could serve in the definition of drought tolerance criteria relevant to varietal selection. (Texte intégral)