Early biochemical criterion of four Fabaceae leguminous plants, were studied, in glasshouse, under water stress condition, in pots on a substrate made up of ¾ of ground and ¼ of sand, with seedlings having two three leaflets leaves. Experimental design was a factorial arranged in a completely randomized block with: four species (Cajanus cajan, Phaseolus lunatus, Tephrosia vogelii and Vigna subterranea), four watering levels: 90 (blank), 60, 30 and 15% of field capacity, replicated five times. Various parameters measured after 15 days of water stress, are content of: chlorophyll a+b, carotenoids, proline, total amino acids, total soluble proteins and total soluble sugars. Results obtained for studied parameters show that water stress differently modifies metabolism of plants according to genotype. Proline content and total soluble sugars content can be used like early indicators and relevant criteria of tolerance to drought, usable in varietal selection and like parameters of improvement of yield in arid areas.