Spontaneous and visually evoked action potentials were recorded from single neurons in cytoarchitectonic area 17 (striate cortex, area V1) of anaesthetized and immobilized cats, prior to, during and after brief reversible inactivation of the ipsilateral postero-temporal visual (PTV) cortex (presumed homologue of primate inferotemporal cortex). Inactivation of PTV cortex resulted: 1) in significant changes in the response magnitude (mostly a reduction) to optimal and/or sub-optimal visual stimuli in over 55 of area 17 cells and 2) significant changes (usually a reduction) in the spontaneous (background) activity of about two-thirds of the cells in which inactivation of PTV cortex significantly affected the magnitude of responses to optimal stimuli. In over 85 of the significantly affected area 17 cells, rewarming PTV cortex to normal temperature (36 degrees C) resulted in the recovery of both the magnitude of responses and the background activity to levels not significantly different from pre-inactivation levels. Irrespective of the significance of changes in the magnitude of responses, in a substantial proportion of area 17 cells, inactivation of PTV cortex resulted in changes in some receptive field characteristics. Thus, there were substantial (20 or more) changes in orientation tuning widths (in over a quarter of the sample) and/or direction selectivity indices (in about a third of the sample). Thus, the feedback signals originating from PTV cortex, like signals originating from some other higher-order visual cortical areas exert a clear modulatory influence on the responsiveness, background activity and some receptive field properties of neurons in the ipsilateral area 17.