In the establishment of cotton suspension culture, we had observed an interesting phenomenon that large-scale cell death occurred when the embryogenic cells were transferred from the medium MS supplemented with IBA 0.5 mg/L to fresh MS medium without IBA. Cytological study and genomic DNA electrophoresis showed that this kind of cell death was accompanied by such morphological characters as chromatin condensation, the maintenance of membrane continuity, a condensed cytoplasm and evident DNA fragmentation of multimers of 140-180 bp. Inhibitor studies suggested the proteolysis and the caspase-like proteases were involved in cell death. These results support that cell death caused by withdrawal of exogenous auxins is a kind of programmed cell death (PCD). So auxin is involved in the regulation of programmed cell death signal transduction pathways, and may be another plant-specific regulator beside ethylene, abscisic acid and gibberellin in PCD.