The response of mung bean (Vigna radiata L. Wilczek cv. Pagasa 3) to three irrigation schedules, two plant densities (PD), and five moisture regimes was studied in 1987 and 1988. Water stress decreased seed yield, pod number, number of seeds per pod, and 1000-seed weight. Number of seeds per pod decreased and number of pods m-2 increased with PD. High plant density (PD2) treatment increased the yield in irrigated and nonirrigated plots compared to low plant density (PD1) treatment. Water use and water use efficiency were high at PD2 when the crop was irrigated at flowering and seed development stages. Although root water extraction efficiency (RWEE) was greater from the upper soil profile (0-60 cm) in all treatments, RWEE was higher in the 60-100 cm soil profile of dry regimes than that of wet regimes. Increase in yield and yield components were highly correlated with water applied in both years. Seed yield was also positively correlated with leaf area index and per cent ground cover while it was negatively associated with specific leaf weight, leaf water potential, osmotic potential, and root length density. The results of the experiment indicated that mung bean can suffer due to water stress when grown in an upland rice soil and that irrigation at flowering and vegetative plus pod development stages can improve seed yield. Effective utilization of subsoil moisture can also be exploited efficiently with higher PD.