We have designed software for an Apple II GS microcomputer allowing simultaneous on-line monitoring of blood glucose level and neuronal firing frequency in experimental rats. Blood glucose level in the carotid blood was continuously measured by a glucose analyzer and digitized through an A/D board. The firing rate of a brain neuron, recorded by a classical technique, was counted by a versatile interface adapter. Both parameters are graphically displayed on the screen. They can also be exported to another computer for off-line analysis. This software is adaptable to other experimental applications in electrophysiology, involving the monitoring of glycemia or other biological parameters.