Listeners were required to detect a mistuning imposed on the center (``target'') component of a harmonic complex consisting of the first seven harmonics of a 500-Hz fundamental. In the standard interval all components were frequency modulated in phase by a 5-Hz sinusoid. In the signal interval the frequency modulation of the target component was inverted in-phase, thereby introducing a mistuning proportional to the depth of FM. For monaural presentation, Carlyon [J. Acoust. Soc. Am. 95, 2622--2630 (1994)] reported a substantial elevation of thresholds in the presence of an unmodulated asynchronous interferer whose frequency was identical to that of the target component. He explained this by assuming that the interferer caused the target component to be perceptually segregated from the remainder of the complex, thereby impairing across-frequency comparisons. The present study investigated the effect of lateralization on the detection of mistuning. Preliminary results of experiment 1 suggest that in the absence of an interferer, presenting the target component contralaterally to the remainder of the complex raises thresholds, but that the task is still possible. Results from experiment 2 indicate that a contralaterally presented interferer impairs performance, a result which is interpreted in terms of auditory streaming.