The aim of the present study is to examine the influence which different concentrations of free fatty acids (FFAs) have on the insulin secretion response of the islets of Langerhans when the culture is prolonged over a week. Animals were killed by decapitation and pancreatic islets of Langerhans isolated. The islets were incubated in enriched RPMI and oleic or linoleic acid was added at concentrations of 0.04, 0.1, 0.375, and 1 mmol/l. The medium without FFAs was used as a control. The culture time was 7 days. For insulin secretion studies, islets were selected after preincubation in batches of six islets in 1 ml of KRB (Krebs-Ringer buffer) containing one of the following: 5.5, 11.1, 16 or 26.7 mmol/l glucose, 10 mumol/l forskolin or 20 mmol/l arginine. The results showed a significant increase in insulin secretion observed after culture with 1 mmol/l oleic and linoleic acid compared to the other concentrations and the control culture for all the secretagogues used. However, at this same concentrations no increase was observed in insulin secretion as the glucose concentration rose, and this was noticeable with linoleic acid at concentrations of 0.375 mmol/l. In conclusion, culture of islets of Langerhans for a week with high concentrations of unsaturated fatty acids produces a hypersecretion of insulin which is not influenced by secretagogues such as glucose, arginine, or forskolin. The loss of gluco-sensitivity may become greater as the degree of unsaturation of the fatty acid used increases.