The cyanide metabolism linked with ethylene biosynthesis was examined with detached satsuma mandarin fruit at different stages of ontogeny. Young immature fruit showed a rapid rise in ethylene production after detaching. Concomitant increases were observed in the β-cyanoalanine synthase activity, ACC and cyanide content with the rise of ethylene production. Moreover, partially yellowing, abscising young fruit on the tree also showed an increased rate of ethylene production, as well as high ACC content and β-cyanoalanine synthase activity. However, the conspicuous increase in ethylene production disappeared as the fruit became larger. Similarly, there was no marked increase in β-cyanoalanine synthase activity. The mechanism of how citrus fruit lose the ability to produce ethylene as they develop remains to be elucidated.