1 Acute and chronic effects of the insulinotropic drug nateglinide upon insulin release were examined in the BRIM-BD11 cell line. 2 Nateglinide (10-400 muM) stimulated a concentration-dependent increase (P <0.05-P <0.001) in insulin release at a non-stimulatory (1.1 mM) glucose concentration. The insulinotropic response to 200 muM nateglinide was increased at 30 mM (P <0.01), but not 5.6-16.7 mM glucose concentrations. 3 In depolarized cells, nateglinide (50-200 muM) evoked K-ATP channel-independent insulin secretion (P <0.05-P <0.001) in the absence and presence of 5.6-30.0 mM glucose (P <0.001). 4 Exposure for 18h to 100 muM nateglinide abolished the acute insulinotropic effects of 200 muM nateglinide, tolbutamide or glibenclamide, but had no effect upon the insulinotropic effect of 200 muM efaroxan. 5 While 18h exposure to 100 muM nateglinide did not affect basal insulin release or insulin release in the presence of 16.7 mM glucose, 25 muM forskolin or 10 nM PMA, significant inhibition of the insulinotropic effects of 20 aim leucine and Maim arginine were observed. 6 These data show that nateglinide stimulates both K-ATP channel-dependent and-independent insulin secretion. The maintained insulinotropic effects of this drug with increasing glucose concentrations support the antihyperglycaemic actions of nateglinide in Type II diabetes. 7 Studies of the long-term effects of nateglinide indicate that nateglinide shares signalling pathways with sulphonylureas, but not the imidazoline efaroxan. This may be significant when considering a nateglinide treatment regimen, particularly in patients previously treated with sulphonylurea.