Single auditory nerve fibers exhibit firing synchronized to one or both phases of periodic AC stimulus currents. Responses to biphasic pulses depend on order and excitation sites of the two phases. Sine and triangle stimuli between 100 Hz and 500 Hz elicit similar response patterns. Responses to square waves are sometimes more synchronized and generally shifted in phase with respect to sine wave responses. Preferred firing phase(s): (1) are largely independent of stimulus intensity; (2) vary among fibers; (3) may shift continuously or discontinuously over several seconds before steady state is achieved. Responses to an unprocessed synthetic vowel stimulus were dominated by pitch period, first formant, and 'spurious' components.