Mitochondrial anaplerosis is important for insulin secretion, but only some of the products of anaplerosis are known. We discovered novel effects of mitochondrial metabolites on insulin release in INS-1 832/13 cells that suggested pathways to some of these products. Acetoacetate, -hydroxybutyrate, -ketoisocaproate (KIC), and monomethyl succinate (MMS) alone did not stimulate insulin release. Lactate released very little insulin. When acetoacetate, -hydroxybutyrate or KIC were combined with MMS, or either ketone body was combined with lactate, insulin release was stimulated 10-20 fold the controls (almost as much as with glucose). Pyruvate was a potent stimulus. In rat pancreatic islets, -hydroxybutyrate potentiated MMS- and glucose-induced insulin release. The pathways of their metabolism suggest that, in addition to ATP, the ketone bodies and KIC supply the acetate component and MMS supplies the oxaloacetate component of citrate. In line with this, citrate was increased by -hydroxybutyrate plus MMS in INS-1 cells and by -hydroxybutyrate plus succinate in mitochondria. The two ketone bodies and KIC can also be metabolized to acetoacetyl-CoA and acetyl-CoA, which are precursors of other short chain acyl-CoAs (SC-CoAs). Measurements of SC-CoAs by LC-MS/MS in INS-1 cells confirmed that KIC, -hydroxybutyrate, glucose and pyruvate increased the levels of acetyl-CoA, acetoacetyl-CoA, succinyl-CoA, hydroxymethylglutaryl-CoA and malonyl-CoA. MMS increased incorporation of 14C from -hydroxybutyrate into citrate, acid-precipitable material and lipids, suggesting that the two molecules complement each other to increase anaplerosis. The results suggest that, besides citrate, some of the products of anaplerosis are SC-CoAs, which may be precursors of molecules involved in insulin secretion.