Objectives: (1) Achieve stable electrode location with respect to an active neuron for reliable acute extracellular recording of human brain cell activity within the pulsating cortex at prescribed depths up to 0.5 cm with minimum tissue damage. (2) Extend this technique to achieve intracellular recording from the pulsating cortex. Methods employed: A microelectrode is supported by a gas bearing assembly and held within the cortex at the desired insertion angle. A fine lead screw is actuated by gas thrust bearings to retain the "floating" action during electrode depth adjustment. An electrocortigram is simultaneously obtained from the adjacent area of cortex. Major findings: The device has been successfully used to obtain high quality extracellular human recordings for prolonged durations. Intracellular recordings using glass micropipette electrodes have been obtained from pulsating monkey brain cortex. Significance: Single-cell electrical recording from cerebral cortex in humans has been limited because of difficulty in atraumatically eliminating the effects of cortical motion. This new method is expected to markedly improve the acquisition of valid information necessary to enhance understanding of brain function and epilepsy. Proposed course: Extension of the technique to intracellular studies in human brain cortex; refinement of technique and apparatus, if necessary; clinical applications; extension of device family for related types of measurement requirements.