The leaching behavior of bituminous coal fly ash has been studied by both field and laboratory tests of ash and water specimens taken from a fly ash disposal site. The site, an abandoned sand quarry which was filled with fly ash, covered, and landscaped in 1974, was instrumented with nine piezometers in January 1978. Six multilevel piezometer nests were installed along the major groundwater table gradient in August 1978. Groundwater specimens have been removed and analyzed periodically since the piezometers were installed. Specimens of ash removed during piezometer installation were tested, first to extract the interstitial water from the ash specimens by a pressure displacement technique, and then to obtain leachates from the ash specimens by shake and column leaching procedures. The results of these tests are used in this paper to compare the composition of leachates derived from the different laboratory leaching methods with the analyses of extracted interstitial waters from corresponding ash specimens and with analyses of groundwater from the field sampling program. The suitability of laboratory leaching tests for predicting the field behavior of coal fly ash is discussed in the light of the results obtained in this comprehensive leaching study.