Although the auditory cortex is known to be essential for normal sound localization in the horizontal plane, its contribution to vertical localization has not so far been examined. In this study, we measured the acuity with which ferrets could discriminate between two speakers in the midsagittal plane before and after silencing activity bilaterally in the primary auditory cortex (A1). This was achieved either by sub-dural placement of Elvax implants containing the GABA_A receptor agonist muscimol or by making aspiration lesions after determining the approximate location of A1 electrophysiologically. Psychometric functions and minimum audible angles were measured in the upper hemifield for 500-, 200- and 40-ms noise bursts. Muscimol-Elvax inactivation of A1 produced a small but significant deficit in the animals' ability to localize brief (40 ms) sounds, which was reversed following removal of the Elvax implants. A similar deficit in vertical localization was observed following bilateral aspiration lesions of A1, whereas performance at longer sound durations was unaffected. Another group of ferrets received larger lesions, encompassing both primary and non-primary auditory cortical areas, and showed a greater deficit with performance being impaired for long (500 ms) and short (40 ms) duration stimuli. These data suggest that the integrity of the auditory cortex is required to successfully utilize spectral localization cues, which are thought to provide the basis for vertical localization, and that multiple cortical fields, including A1, contribute to this task.