The effects of plant water stress imposed at vegetative, flowering, and fruiting stages of four cultivars of tomato (Lycopersicon esculentum Mill.) on net photosynthetic rate (PN), stomatal conductance (gs), transpiration rate (E), osmotic adjustment, and crop water stress index (CWSI) were investigated. Osmotic adjustment was the highest in cv. Arka Meghali, followed by cv. RFS-1. CWSI was lowest in cv. Arka Meghali and highest in cv. Pusa Ruby. Significant reduction in gs, E, and PN was observed in all the cultivars. The maximum reduction in E was observed in cv. Arka Saurabh during the fruiting stage (62.4 %) and maximum reduction in PN at the flowering stage in Pusa Ruby (53.1 %). Maximum PN was observed in Arka Meghali under water stress. The values of internal CO2 concentration (Ci) did not follow the decrease in gs which might be taken as an indication of mesophyll (non-stomatal) limitation to PN. Magnitude of PN decrease accompanying gs reductions varied in the four cultivars. Arka Meghali which had highest rate of gas exchange efficiency (PN/gs) under water deficits can be recommended for rainfed cultivation. and N. K. Srinivasa Rao, R. M. Bhatt, A. T. Sadashiva.