This report describes the temporal patterns of discharges of single nerve fibers recorded by a microelectrode in the modiolus in response to short‐term dc (5‐sec) and ac stimulation delivered across scala media in the basal turn of the guinea pig's cochlea. These electrical stimuli produce increases or decreases in discharge rates, depending on the polarity of the current, but do not show adaptation effects when the current strength is moderate. Currents with scala vestibuli positive with respect to scala tympani (SV‐ST) are usually excitatory, while currents with ST‐SV produce reductions in discharge rate. The effect of a given polarity is found to depend on a unit's prestimulation spontaneous rate. When electrical stimulation is added to acoustic stimulation, the intensity function at best frequency is shifted laterally, with the direction of the shift depending on current polarity. When the effects of two sources of stimulation, acoustic and electric, are added, the maximum discharge rate seen for acoustic inputs is not altered; it only occurs at a lower strength of the acoustic signal. The addition of electrical stimulation to acoustic frequencies other than best frequency may show different effects.