The vast majority of the saline agricultural wastewater that is presently being generated within the San Joaquin Valley is discharged to the San Joaquin River. As the quantity of this waste increases, the waste load on the river would reach a point of extreme unacceptability. The San Joaquin River would become saline and downstream users would be deprived of a usable water supply. For these reasons, a system is now under construction to collect much of the saline drainage and transport it to a 'safe' disposal site. The material presented describes the operation of upflow anaerobic filters operated to determine if nitrate-nitrogen could be efficiently removed from the subsurface agricultural drainage. Filters of three sizes (4-, 18-, and 36-inch diameters) were operated under field conditions.