Three 2-methoxy-3-alkylpyrazines (MPs) in Japanese red wine and grape samples were determined by GC-EIMS, using 2-methyl-3-n-propylpyrazine as an internal standard. MPs in the Cabernet Sauvignon red wines were derived not only from the pulp but also from other parts of the grape berries. All of the Cabernet Sauvignon red wines made annually from 1975 to 1994 contained 2-methoxy-3-isobutylpyrazine (isobutylMP), although those made from well-ripened grapes had a low isobutylMP level. It is suggested that the climatic conditions of September might effect the isobutylMP level of Cabernet Sauvignon grapes and red wines. The mean isobutylMP level of Cabernet Sauvignon, Cabernet Franc, and Merlot Japanese commercial red wines was significantly higher than the mean isobutylMP level of Muscat Bailey A and Zweigeltrebe.