The asynchronous programmed cell death (PCD) in different regions of the cotton cotyledon was studied during senescence. We showed that changes in chlorophyll contents do not occur at the same time in different parts of the cotyledon. By using light microscopy (LM) and the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end in situ labelling (TUNEL) methods, the symptoms of cell death were detected in cotyledon margins earlier than in the central part. DNA ladders were detected by gel electrophoresis in senescent cotyledon margins and in the centre respectively, but not in the whole cotyledons.