During a 3-yr study, we investigated the effects of grapevine,Vitis viniferaL., irrigation management on the abundance of the western grape leafhopper,Erythroneura elegantulaOsborn and a variegated grape leafhopper,E. variabilisBeamer, at two locations in the San Joaquin Valley of California. Irrigation treatments ranged from 40 to 120% replacement of the expected nonstressed crop evapotranspiration (EToc). Densities of both species were significantly lower on vines in the low irrigation treatments (0.4, 0.6, and 0.8 EToc), than on vines that received maximum water allotments (1.0 and 1.2 EToc). Leafhoppers tended to be more numerous on the shaded side of the vines than on the sunlit side.E. elegantulaattained a maximum average density of 15 nymphs per leaf at Westside in 1984, whereas a maximum of 23 nymphs per leaf was recorded forE. variabilisat Kearney. There was greater variation in leafhopper densities in response to irrigation treatments at Westside than at Kearney, an effect believed to be the result of differential water holding capacities of the respective soils at each location. Restricted available water can affect vine water status and alter characteristics of the microenvironment, including canopy temperature and humidity. Both transient and long-term irrigation effects can contribute to fluctuations in leafhopper abundance.