Pancreatic somatostatin cells have been studied in human neonates and adults using an immunoperoxidase technique. Their volume density in the head, isthmus, corpus and tail of the gland has been estimated by morphometry. Somatostatin cells were about 20 times more frequent in the neonate (5% of all pancreatic cells) than in the adult (0.23%). Their distribution between the different zones of the pancreas showed few differences except for the lobe of the head rich in PP cells, where the volume density of somatostatin cells was 40% lower.