The release of cytochrome c from mitochondria induced by 10 microM thapsigargin was linked to rapid loss of the mitochondrial membrane potential whereas that induced by 50 nM staurosporine was mediated by Bax activation and occurred in polarized mitochondria. Similar levels of cytochrome c were observed when induced by either thapsigargin or staurosporine indicating that the release magnitude was independent of the mechanism involved in membrane permeabilization. In any case caspase 3 activation was subsequent to cytochrome c release. Mitochondrial dysfunction and release of cytochrome c occurred earlier when induced by thapsigargin even though morphological alteration of the cell and chromatin condensation were developed earlier in the presence of staurosporine. In addition, a general and irreversible caspase inhibitor did not protect against chromatin condensation induced by staurosporine. It is also shown that earlier mitochondrial damage does not always correlate with earlier cell demise. This can be attributed to the existence of alternative caspase-independent cell death programmes.