This study was conducted to determine the effects of different water and nitrogen application levels on drip-irrigated tomato plants. The amount of water usage was based upon the pan evaporation from a screened (class "A") evaporation pan. The treatments consisted of two irrigation intervals (I1= 5 days and I2= 10 days), three plant-pan coefficients (K(cp)1= 0.50; K(cp)2= 0.75 and K(cp)3= 1.00) and three nitrogen (N) levels (N0 = 0, N1= 80 and N2= 160 kg ha(-1)). The I, K-cp and N levels affected the tomato yields and water usage efficiencies, however the effects of nitrogen applications were found to be greater than those of the other applications. Consequently, to reach the maximum tomato yields under similar climate and soil conditions, plant-pan coefficients (K-cp) and nitrogen values should be equivalent to 1.00 and 160 kg ha(-1), respectively.