Thaumatin-like proteins and chitinases are the main pathogenesis-related (PR) proteins found in grapes, grape juice and wine and are responsible for protein haze formation in bottled white wine during storage and transport. We have studied the effect of the content of both thaumatin-like proteins and chitinases on protein instability of Sauvignon blanc (clones 1, 107 and 242) and Chardonnay (clones 4, 5, 75 and Mendoza) grape juices from both a warm and a cold production zone in the Casablanca Valley, Chile. The PR proteins were identified and quantified by reversed-phase liquid chromatography (RP-HPLC). Protein instability was determined using a heat test and was expressed in nephelometric turbidity units (NTUs). Thaumatin-like (TL) proteins were identified as the major PR proteins present in all grape juices studied. Three TL proteins were identified and named Vitis vinifera thaumatin-like proteins 1, 2 and 3 (VVTL1, VVTL2 and VVTL3). Chitinase A (ChitA) was identified in the Sauvignon blanc and Chardonnay grape juices, and chitinase B (ChitB) was found only in Chardonnay grape juices. Significant differences in the protein content and in the type of protein were observed between grapes from different production zones and between grapes of different varieties, respectively.