The measurements of intrinsic unitary and macroscopic properties of potassium channels in motoneurones constitutes an important step in the characterization of cellular function. A number of potassium currents contribute to the integrated function of motoneurones and this review considers the properties of the inward rectifier (Ih-type), calcium-dependent (BK- and SK-types), delayed rectifier, transient outward, and leak currents. The modification of channel properties by agents such as serotonin and thyrotropin-releasing hormone is likely relevant to modulation of motoneurone function. Indeed, even during the course of normal cell development, the expression and properties of particular potassium channels can undergo considerable changes, which would be manifested as altered firing patterns and excitability of motoneurones. Brainstem and spinal cord slices have considerable utility for electrophysiological studies and have been used in recordings from spinal, hypoglossal and facial motoneurones. New procedures have also been developed which would enhance the purification of cultured motoneurones for patch-clamp experiments.