Diurnal patterns of leaf water potential (ΨW), canopy net photosynthetic rate (P(N)), evapotranspiration rate (E), canopy temperature (T(c)), and water use efficiency (WUE) of clusterbean [Cyamopsis tetragonoloba (L.) Taub., cv. Desi] were studied at six phenological stages of plant development under field conditions at CCS Haryana Agricultural University, Hisar. The highest P(N), E, and WUE were observed at pod initiation stage (61 DAS). Daily maxima of P(N) were usually between 11:00 to 14:00 h while those of E and WUE between 12:30 and 16:00 h. P(N) was mainly dependent on photosynthetically active radiation and E on air temperature (T(a)) but the relationships varied at different growth stages. WUE declined with the increase in T(a). At mid-day, ΨW was highest during pod initiation.