A recent study by Corteen & Wood (1972) suggested that material of which the subject was unaware, on the unattended channel in dichotic listening, may be processed for meaning yet fail to interfere with the primary task of shadowing prose on the attended channel. The experiment reported here examines the converse hypothesis that this non-interference between attended and unattended information would fail to occur if the primary task could be facilitated by information on the unattended channel. Mackay (1973) has provided some evidence to support this hypothesis using verbal material on both channels, thus involving, presumably, only one hemisphere. By using stimulus materials on the two channels that are believed to be processed by the right and left hemispheres respectively, a second hypothesis, that facilitation by the unattended input would depend upon laterality differences, was also tested. Considerable support was found for both hypotheses.