We investigated attentional modulation of auditory cortex in monkeys, trained to alternate between auditory and visual discriminations. Laminar event related potential (ERP), current source density (CSD) and multiunit activity (MUA) profiles were obtained by sampling neural activity during penetrations of auditory cortex with linear array multielectrodes. Attention effects were defined by comparing cortical response profiles evoked by tones and more complex stimuli when attended, with the responses to the same stimuli when ignored. Analyses of averaged responses produced 2 findings of general interest. First, attentional modulation begins 20 ms or more after the onset of the local sensory response, and has a clear bias toward the supragranular laminae, with little or no impact on short latency activity in Lamina 4. This pattern of findings is consistent with a "stimulus-driven" feedback model of attention. Second, attention produced a relative negativity in the supragranular ERP at many sites. The CSD profile revealed local contributions to the effect. This may relate to the Processing Negativity observed under similar experimental circumstances in the human scalp ERP. Attentional modulation of oscillatory activity was investigated by analyzing single trial responses using Fast Fourier Transform (FFT) and Wavelet Analysis routines. These analyses revealed attentional modulation across a range of EEG frequencies, including both the lower frequencies in which stimulus/phase-locked activity forms significant contributions to the averaged ERP and higher (gamma) frequencies. There is also an indication of an anticipatory attentional modulation of baseline activity. Local visual responses were detected and appeared to be modulated by attention.