Spike potentials were recorded from single fibres in the auditory nerve of the pigeon. In responses elicited by tonal stimuli, the timing of each spike relative to stimulus waveform was measured and period histograms were constructed. Phase locking of spikes was estimated in terms of a synchronicity index obtained by vector addition within the period histogram. A second measure of synchrony in the spike responses was obtained, that of temporal dispersion. For a population of fibres, vector strength of phase locking decreased for frequencies above 1 kHz, as reported for several other species. Temporal dispersion, however, also decreased with frequency, indicating enhanced temporal synchrony as frequency increased within the bandwidth of phase locking. The upper frequency limit of phase locking appears to depend on irreducible jitter of biological origin in the timing of spikes. For individual fibres, the bandwidth of synchronization of spikes consistently exceeds the response area, covering in addition the areas of suppression adjacent to the response area. Spike trains suppressed by a tonal stimulus become synchronized to that stimulus. Phase angles of synchronized responses systematically change as a function of tone level, when tone frequency is above or below CF, as reported for other avian species. Synchronicity and phase angle intensity functions are quite independent of spike rate intensity functions.