Normal-phase liquid chromatography/mass spectrometry (LC/MS) was used to determine the levels and fate of procyanidins in frozen and canned Ross clingstone peaches as well as in the syrup used in the canning over a 3 month period. Procyanidin oligomers, monomers through undecamers, were identified in Ross clingstone peaches. Optimized methods allowed for the quantitation of oligomers through octamers. The profile of procyanidins in peaches is similar to profiles found in grapes, chocolate, and beverages linked to health benefits such as tea and wine. The monomer content in frozen peeled peaches was found to be 19.59 mg/kg. Dimers (39.59 mg/kg) and trimers (38.81 mg/kg) constituted the largest percent composition of oligomers in the peaches. Tetramers through octamers were present in levels of 17.81, 12.43, 10.62, 3.94 and 1.75 mg/kg, respectively. Thermal processing resulted in an 11% reduction in monomers, a 9% reduction in dimers, a 12% reduction in trimers, a 6% reduction in tetramers, and a 5% reduction in pentamers. Hexamers and heptamers demonstrated an approximate 30% loss, and octamers were no longer detected. Analysis of the syrup after thermal processing indicates that there is a migration of procyanidin monomers through hexamers into the syrup that can account for the losses observed during the canning process. Storage of canned peaches for 3 months demonstrated a time-related loss in higher oligomers and that by 3 months oligomers larger than tetramers are not observed. At 3 months postcanning, levels of monomers had decreased by 10%, dimers by 16%, trimers by 45%, and tetramers by 80%. A similar trend was observed in the canning syrup.