To determine the mechanism of inhibition of anthocyanin accumulation in the skin of grape berries due to high temperature, the effects of high temperature on anthocyanin composition and the responses in terms of gene transcript levels were examined using Vitis vinifera L. cv. Cabernet Sauvignon. High temperature (maximum 35 degrees C) reduced the total anthocyanin content to less than half of that in the control berries (maximum 25 degrees C). HPLC analysis showed that the concentrations of anthocyanins, with the exception of malvidin derivatives (3-glucoside, 3-acetylglucoside, and 3-p-coumaroylglucoside), decreased considerably in the berries grown under high temperature as compared with the control. However, Affymetrix Vitis GeneChip microarray analysis indicated that the anthocyanin biosynthetic genes were not strongly down-regulated at high temperature. A quantitative real time PCR analysis confirmed this finding. To demonstrate the possibility that high temperature increases anthocyanin degradation in grape skin, stable isotope-labelled tracer experiments were carried out. Softened green berries of Cabernet Sauvignon were cut and aseptically incubated on filter paper with 1 mM aqueous L-[1-(13)C]phenylalanine solution for 1 week. Thereafter, the changes in (13)C-labelled anthocyanins were examined under different temperatures (15, 25, and 35 degrees C). In the berries cultured at 35 degrees C, the content of total (13)C-labelled anthocyanins that were produced before exposure to high temperature was markedly reduced as compared with those cultured at 15 degrees C and 25 degrees C. These data suggest that the decrease in anthocyanin accumulation under high temperature results from factors such as anthocyanin degradation as well as the inhibition of mRNA transcription of the anthocyanin biosynthetic genes.