The aim of this work was to simultaneously study the secretion of islet amyloid polypeptide (IAPP) and insulin from isolated rat pancreatic islets in vitro. For examination of stimulated β-cells, nutrient secretagogues (16.7 mM glucose, 10 mM leucine + 2 mM glutamine), phosphodiesterase inhibition (5 mM theophylline), a sulphonylurea (0.5 μg/ml glipizide), a non-nutrient amino acid (10 mM arginine), cholinergic stimulation (0.1 mM carbamylcholine) and insulinotropic peptides (0.1 μM vasoactive intestinal polypeptide and 0.1 μM glucagon), were used. For β-cell suppression glucose phosphorylation inhibition (10 mM mannoheptulose), depletion of extracellular calcium, activation of the ATP-regulated K⁺-channel (0.5 mM diazoxide), adrenoreceptor stimulation (3 μM adrenaline), paracrine modulation (0.1 μM somatostatin), short-term treatment with a selective β-cytotoxin (1.1 and 2.2 mM streptozotocin) and long-term treatment with a cytokine (25 U/ml interleukin-1β), were studied. The compounds with known effects on insulin secretion exerted their expected actions and this was paralleled by similar relative changes, with a possible exception for glucagon, in the IAPP secretion. The ratio of IAPP/insulin released did not change significantly under any of the tested experimental conditions, except for a slight increase following carbamylcholine stimulation. On a molar basis approx. 1% of IAPP was released when compared with insulin. These results are consistent with the hypothesis that the regulation of IAPP secretion from β-cells of isolated rat pancreatic islets is essentially regulated by the same mechanisms as insulin secretion.