Senescence in excised orange leaves is characterized by a loss of chlorophyll, particularly chlorophyll, and an increase in amylolitic activity, which appears to be the most sensitive index to detect senescence. On the other hand, leaf proteins do not decrease appreciably, which contrasts with the behaviour of attached leaves and suggests that proteolysis does not play a central role in the senescence of these leaves but is a consequence of competition from nearby actively growing organs. Gibberellic acid and indole-3-acetic acid, but not kinetin, are able to delay leaf senescence, the effect of the former being more appreciable. GA delays the loss of chlorophyll for more than a fortnight, but only delays the characteristic rise in amylase activity for about 48 h.