Subjects compared pitches of a standard tone and a comparison tone separated by 1,300-3,000 msec and responded according to whether the comparison tone sounded higher or lower in pitch than the standard tone. Three interfering tones at 300-msec intervals were presented before each pair of tones. Their pitch range varied, being either below or above the pitch of the standard tone; in some of the trials, their pitches were identical to the pitch of the standard tone (no interference). The highest error rate in performance was found when the interfering tones and the comparison tone deviated in the same direction in pitch from the standard tone. In turn, their deviations in the opposite directions resulted in the lowest error rate. This effect was not found to be dependent on whether the interfering tones were randomly ordered or monotonically ordered, together with the standard tone, into melodically ascending/descending sequences. An intermediate error rate in performance was found when the interfering tones and the standard tone were identical. The results support earlier hypotheses, presented in the context of retroactive interference, by demonstrating proactive interference of a tone sequence at the level of representations of individual tones.