Cues for listeners' assignment of melodic structure are investigated in music performance. Performers' interpretations of musical structure can influence listeners' perceptions, especially when structural relations among musical events are ambiguous. Performances recorded on a computermonitored acoustic piano were compared with each performer's notated interpretations of melody. Small timing changes (20-50 ms) marked performers' melodic intentions; events interpreted as melody (the most important voice) preceded other events in chords (melody lead). The emergence of melody leads was investigated in successive performances of unfamiliar music: melody leads were larger in experts' than in students' performances, but students showed more increase with practice. In additional experiments, performances of the same music with different melodic interpretations displayed the melody lead in different amounts, which subsequently affected listeners' perceptions of melodic intentions. Subtle expressive cues in music performance arise from individual interpretations and can aid listeners in determining musical structure.