The histological distribution of insulin like growth factor 1 (IGF 1) receptors in the rat gut was studied. Immunostaining of IGF 1 receptors identified localisation on the villus epithelium, in the crypts, and in Brunner's glands of the small intestine. These tissues represent areas of high cell growth/differentiation, division, and macromolecular synthesis respectively, which constitute biological activities long associated with IGF 1. Cellular localisation of IGF 1 receptors was seen in the lamina propria by IGF 1 receptor immunostaining and ligand binding of biotinylated IGF 1. IGF 1 receptor immunostaining in the spleen showed receptor localisation to the splenic pulp thus pointing to macrophages as the possible IGF 1 receptor positive cells in the lamina propria. The results further implicate IGF 1 as an important growth factor in gut maintenance.