Sulfhydryl compounds and sulfhydryl reagents were applied to Bartlett pears to test their effect on the onset of ripening. The ripening parameters tested were softening and the evolution of CO2 and ethylene. Application of the sulfhydryl compounds cysteine and dithiothreitol resulted in the inhibition of ripening. Sulfhydryl reagents, including alloxan and N-ethylmaleimide, promoted the ripening process. The results suggest that the onset of ripening is influenced by a decline of sulfhydryl gradients in fruit.