To determine some of the factors which contribute to the color changes in wines during processing and aging, the effects of pH and temperature were investigated on the anthocyanidin-3,5-diglucosides, the main pigment constituents of Vitis labrusca grapes and their hybrids. The 3-5-diglucosides of cyanidin, peonidin, delphinidin, petunidin and malvidin, isolated from Seibel No. 9549 grapes were incubated in buffer solutions with various pH9s (1.5, 3.0, 4.0, 5.0, 6.0 and 7.0) at temperatures ranging from 20 to 90°C, and destruction of the pigments was determined spectrophotometrically. The pigments were most stable at pH 5.0, where they are rapidly converted to the colorless carbinol base form. The stability of the pigments increased with increasing methoxyl substitution and decreased with increasing hydroxyl substitution in the molecule. Malvidin-3,5-diglucoside is the most stable, followed by peonidin, petunidin, cyaniclin and delphinidin-3,5-diglucosides.