A heterogeneity in the cellular composition of the endocrine pancreas, with a preponderance of pancreatic polypeptide cells in the lower head region, has been linked to the dual origin of the organ. The pancreas develops from a ventral bud thought to contain potential pancreatic polypeptide cells and a dorsal bud contributing the non pancreatic polypeptide cells. This does not explain, however, several anomalies including the results reported here of a homogenous distribution of non insulin cells in the foetal baboon whilst the adult pancreas exhibits a heterogenous distribution with the pancreatic polypeptide-rich area in the lower head of the pancreas. If this heterogeneity is associated with the dual origin of the pancreas, it would be expected to be more pronounced in the foetus. The anomalies could be explained if both primordial buds contained progenitor cells of all endocrine cell types which could be expressed to meet the requirements of the body at any particular time.