The distribution of acetylcholinesterase (AChE) at the ultrastructural level was investigated in normal and in pancreatic fragments transplanted for 56 days into the anterior eye chamber of heterologous rats using enzyme cytochemical methods. Acetylcholinesterase reaction products were seen on the basal surface of the acinar cells in normal pancreas. Acetylcholinesterase enzyme activity was also detected on the axolemma of the surviving nerve fibres. This enzyme reaction product forms alternating thick and thin bands on the axolemma. Some of these AChE-positive nerve fibres accompany blood vessels that also survive after transplantation. AChE were seen in cytoplasm adjacent to the surviving alpha and pancreatic polypeptide cells. We conclude that the ability of some neurons and cells to produce and or store acetylcholinesterase is still retained after transplantation of pancreatic tissue into the anterior eye chamber of rats.