Single-channel Ba2+ current recordings have been made from the insulin-secreting cell line RINm5F with the patch-clamp technique. Depolarization evokes opening of Ca2+ (Ba2+) channels with a relatively high conductance (30 pS) and during the 200 ms depolarizing pulses there is no inactivation. The threshold is high as 50 mV depolarization from the resting membrane potential of -70 mV is required for any channel opening to occur. Glyceraldehyde, a substance evoking insulin secretion from the RINm5F cells, enhances the voltage-activated Ca2+ channel opening by increasing the mean open time and decreasing the longer of the two mean shut times and also decreases the voltage threshold for channel opening.