Restrictions to attentional capacity are revealed by the interference that commonly results when two sensory inputs must be identified at the same time. To investigate this phenomenon within and between modalities, we presented streams of visual and/or auditory inputs, containing occasional targets to be identified and recalled. For two visual or two auditory streams, identification of one target produced a sustained reduction in the ability to identify a second, the period of interference lasting for several hundred milliseconds. Subjectively, when attention was assigned to one target it was temporarily unavailable for another. In contrast, there was no such time-locked interference between targets in different modalities. The results suggest a modality-specific restriction to concurrent attention and awareness; visual attention to one simple target does not restrict concurrent auditory attention to another.