Chromogranin A is a 49 kDa acidic protein that consists of 439 amino acids encoded on chromosome 14. Chromogranin A has been identified in anumber of normal and neopastic endocrine tissues. It was demonstrated that an elevated circulating chromogranin A level would be a marker oftumors of neuroendocrine origin. However, the most significant clinical use of chromogranin A is related to the diagnostic procedure in patients ofpheochromocytoma. The following is a short summary of potential use of chromogranin A.1. A very sensitive (83%) and highly specific (96%) marker in the evaluation of actual or suspected pheochromocytoma. Drugs commonly employedin the diagnosis or treatment of pheochromocytoma has little effect on the plasma chromogranin A level, which is great advantage of measuringchromogranin A over catacholamines.2. To ascertain the source of a tumor. A high chromogranin A level indicates that the tumor arises from neuroendocrine tissues.3. Endocrine tumors that do not produce their specific hormones, for example, calcitonin negative but chromogranin A positive C-cell carcinoma;zero-cell carcinoma; beta-cell carcinoma; parathyroid carcinoma.