Glucose-induced insulin secretion from pancreatic &cells is known to involve an influx of calcium through voltage-dependent Ca channels. Recently we have recorded singlechannel currents flowing through &cell Ca channels using the outside-out configuration of the patch-clamp technique and Ba2+ as the charge carrier.'Only one type of Ca channel was observed. This had a single-channel slope conductance of 24 pS in 110 mM Ba2+, was sensitive to dihydropyridines, and was blocked by micromolar concentrations of Cd2+. These properties are consistent with the view that this Ca channel is of the L-type (for terminology see Nowycky et aL2). The outside-out patch configuration involves the replacement of the cytosol with an artificial solution and is therefore unsuitable for investigations of the metabolic regulation of the Ca channel. For these studies we have used cell-attached patches, because Ca channels are then exposed to their normal internal environment. We present here preliminary cellattached recordings of single Ca channels in mouse pancreatic &cells, using previously published methods.'