We used a retrograde marker, rhodamine-labeled fluorescent latex microspheres and the enzyme papain to isolate a group of identified, dorsal horn projection neurons from rat spinal cord. This method has allowed us to study the electrical properties of these acutely dissociated cells with patch-clamp techniques. It will also provide us the opportunity to understand the transmitter responses of these neurons that had not undergone culturing manipulation. The isolated projection cells have a short-lasting action potential and fire repetitively under a sustained depolarization. The ionic conductance mechanisms underlying the action potentials were studied under voltage-clamp conditions. Voltage-dependent inward sodium, inward calcium, outward potassium and calcium-activated potassium currents were observed in these cells.