In this chapter we report on the characterization of linear antigenic sites of human chromogranin A (CgA), a useful tissue and serum marker for neuroendocrine tumours and a precursor of many biologically active peptides. The epitope mapping of CgA has been carried out by peptide microarrays on glass slides coated by a copolymer of N,N-dimethylacrylamide (DMA), N,N-acryloyloxysuccinimide (NAS) and [3-(methacryloyl-oxy) propyl] trimethoxysilyl (MAPS). The microarray support provided sufficient accessibility of the ligand, with no need for a spacer, as the polymer chains prevent interaction of immobilized peptides with substrate. In addition, the polymeric surface constitutes an aqueous micro-environment in which, despite peptide random orientation, linear epitopes are freely exposed. The results reported are in accordance with those obtained in conventional ELISA assays using biotinylated and non-biotinylated peptides.