A method and apparatus for determining the availability of unipolar and/or bipolar pacing/sensing paths in a body-implantable cardiac pacing system. In one embodiment, a pacemaker system includes impedance monitoring circuitry for periodically measuring impedance between pairs of electrodes that are potentially available for pacing and/or sensing. This impedance monitoring circuitry includes circuitry for delivering excitation pulses between pairs of potentially available electrodes (including the pacemaker canister in the case of unipolar pacing or sensing), and for monitoring the current and voltage between those pairs of electrodes during delivery of an excitation pulse. Availability of a pair of electrodes for pacing and/or sensing is indicated if the impedance between a pair of electrodes is found to lie within a predetermined range. Detection of availability of a particular pair of electrodes is used initially as an indication that the pacing system has been implanted, and is also used to distinguish between unipolar and bipolar leads in the pacing system.