Phytoalexins of Musa balbisiana [BBB] cv Saba sa Hapon and cv Mundo fruits were compared with those of M. acuminata [AAA] cv Buñgulan fruits. Phytoalexins induced by wound and inoculation of Colletotrichum musae in these two cultivars were the same as those of Buñgulan. In the course of analysis of the phytoalexins, 2-phenyl-1,8-naphthalic anhydride, 2-(4'-methoxyphenyl)-1,8-naphthalic anhydride, and 1,2,3,4-tetrahydro-6,7-dihydroxy-1-(4'-hydroxycinnamyliden)naphthalen-2-one were found as new phytoalexins of banana fruits. This latter compound is probably a biosynthetic intermediate of phenylphenalenones in banana fruits.