Penicillium digitatum Sacc., has been investigated by a number of workers (1), but its pathway of biosynthesis and importance in fungal metabolism have yet to be defined. Factors affecting growth of the fungus have been studied intensively and a satisfactory medium has been developed (2, 7). The importance of zinc and yeast extract as growth factors in the medium was demonstrated by Pratt (7) and later workers (3, 9). In these studies, ethylene production and growth were assumed to be (lirectly related. More recently, Spalding and Lieberman (8) reported that yeast extract exerts a much greater stimulatory effect on ethylene production than on growth. The present report will consider the effect of yeast extract components on ethylene production by P. digitatlum. Variation found to be associated with the source of fungal inoculum and cultural conditions will also be discussed.