Specific antisera were raised against synthetic peptide fragments of bovine chromogranin A. The soluble proteins of bovine chromaffin granules were subjected to two-dimensional immunoblotting with these antisera. The endogenous breakdown products of chromogranin A gave distinct patterns of immunostaining which enabled us to correlate these peptides with defined regions of the chromogranin A molecule. The results establish that within chromaffin granules degradation of chromogranin A by the endogenous proteases can start either at the C- or the N-terminal site.