Programmed cell death (PCD) during which up to 50% of the neurons die in a certain period of time, occurs in the developing nervous system. Proteases, among them CASPASEs, are known to be involved in cell death. To investigate if any specific protease (s) has a key role in PCD, chicken embryos were treated daily from E6-E9 with different protease inhibitors in this study. Among the inhibitors available in market, those for the CASPASE inhibition in general and for the inhibition of CASPASE 8, CASPASE 9 and calpain were used. Embryos were killed at E10 and neurons were counted in cilliary ganglia (CG). As expected, there was a significant increase in neuron numbers in CGs of embryos treated with a general CASPASE inhibitor. Interestingly, among the other CGs, there was a significant increase in neuron numbers only in those treated with CASPASE 9 inhibitor. These results suggest a key role of CASPASE 9 in the intracellular pathway of PCD.