Barium currents flowing through single Ca2+ channels were recorded from outside-out patches isolated from mouse pancreatic B-cells. Only one type of Ca2+ channels was observed. In 110 mM Ba2+, the single channel conductance was 24pS (at negative membrane potentials) and the current amplitude at 0 mV was -0.7 pA. Channel openings were activated by depolarisations more positive than -30 mV and showed little inactivation during 200 ms pulses. Open times were increased by BAY K 8644 an decreased by micromolar Cd2+. Channel activity was subject to rundown in excised patches and little activity remained after 10 min. These properties resemble those of L-type Ca2+ channels in other tissues. It is suggested that this Ca2+ channel participates in the generation of the B-cell action potential and mediates the increase in Ca2+ influx required for insulin secretion.