The biosynthesis of pisatin, an antifungal compound produced in Pisum sativum L. tissue infected with various parasitic organisms or treated with chemicals, was investigated. l-phenylalanine-[U- 14C]methionine-methyl- 14C, cinnamic acid-COOH- 14C and acetate-1- 14C administered to excised pea pods were incorporated into pisatin. Evidence is presented that implicates acetate and cinnamic acid as precursors of pisatin.