During leaf senescence protein degradation is induced. In order to obtain information on the enzymes involved in this process, a study was initiated to identify and characterize proteases induced in artificially senescing parsley leaves. A 70 kDa serine protease (EC 3.4.21) was identified by an activity gel assay. This protease, present in low level in young leaves, was found to be considerably induced in parallel to the advance of senescence and the reduction in the protein content of the leaves. A high correlation between progress of senescence and the induction of the 70 kDa serine protease was demonstrated. Treatments with CO2 or gibberellic acid, which retard senescence, reduced the protease's activity, whereas acceleration of senescence with ethylene enhanced it.