Previous in vivo studies have suggested a long term regulatory role for insulin in the exocrine pancreas. Furthermore, we reported that pancreatic acini have specific receptors for IGF I and II, and using different techniques (acid washing, trypsinisation, electron microscope autoradiography), that CCK8 reduces the internalisation of IGF II. To now directly study the long term role for IGF and insulin in the exocrine pancreas we used AR42J cells, a rat cell line that is derived from a transplantable tumour of the acinar pancreas. Hormone binding studies with 125I-labelled hormones indicated that those cells have insulin receptors, relatively fewer receptors for IGF II but in contrast with normal acini no detectable IGF I receptors. Insulin at concentrations as low as 1 nm stimulated the growth of AR42J cells, as measured by an increase in cell number, DNA and protein content. At 100 nM insulin had maximal effects stimulating the growth by about 50%. IGF I and II had only very weak growth promoting effects probably due to their interaction with the insulin receptor. Additionally insulin increased amylase synthesis over the same concentration range that it stimulated growth. But immunoprecipitation studies revealed that insulin induced a selective increase of amylase synthesis over general protein synthesis. These studies indicate, therefore, that insulin is a growth promoting hormone for AR42J cells and that additionally it seems to specifically regulate amylase synthesis. The role for the IGFs in the exocrine pancreas, however, still remains to be determined.