Owls localize sound sources precisely for hunting mice in darkness. The main cue for sound localization in azimuth is the interaural time difference (ITD). The ITD is computed online in the 3rd order auditory relay station, nucleus laminaris (NL). NL neurons serve as coincidence detectors of binaural signals for ITD computation. Although the cellular mechanism for coincidence detection has long been the subject of discussion and modeling, coincidence detection has not been directly observed in vivo. We developed a new technique for intracellular recording from owl's NL neurons in vivo by using coaxial glass electrodes in which one (microelectrode) was inserted into a patch-electrode type capillary. These two electrodes were advanced by two independent microdrives. NL neurons produced small action potentials and sinusoidal oscillatory potentials whose frequency corresponded to the stimulus sound. These sound analogue psps changed their amplitudes with ITD. The number of spikes evoked by sound changed with the amplitude of the sound analogue psps. Carr et al (1993) reported that the initial segment of owl's laminaris neurons was covered with myelin, and they inferred from this anatomical feature that the spike initiation site of the owl's laminaris neuron is not the initial segment but the 1st node of Ranvier. The small spike observed in this study supports their interpretation that the site of spike generation is separated from that of synaptic integration in the owl's NL neurons. [Jpn J Physiol 54 Suppl:S23 (2004)]