Recordings were made under ketamine anesthesia from 385 neurons in primary auditory cortex in adult cat and from 265 neurons in 10-55 day old kittens. The temporal Modulation Transfer Function for the response to repetitive click stimuli peaked at 8 Hz. After a click a suppression period of 130- 155 ms in duration, depending on click-rate, was observed. This suppression period limited the response to high click rates and thereby determined the 'resonance' in the click response. The suppression duration in kittens decreased in exponential fashion toward the adult value with a time constant of about 1 month. After the one second duration click-trains an oscillatory rebound with a mean period of 113 ms was observed in about 60% of the recordings in the adult cat. Spontaneous activity showed in about 30% of the neurons an oscillatory autocorrelogram with an average period of 126 ms in the adult cats and 170 ms in kittens.