This study investigated the role of concurrent musical parts in pitching ability in sight-singing, concentrating on the effects of melodic and harmonic coherence. Twenty-two experienced singers sang their part twice in each of four novel chorales. The chorales contained either original or altered melody and original (tonal) or altered (atonal) harmony. Participants also performed an interval-singing task. Alterations from the original in both melody and harmony increased pitching errors in sight-singing. These results indicate respectively that pattern recognition and harmonic prediction are integral to sight-singing ability. Singers made fewer errors on the second reading, showing the role of familiarity. Error rate correlated with interval-singing performance. Less skilled sight-singers were significantly more affected by a disruption in harmony than were better sight-singers. The results suggest an increasing role for internal auditory representations with increasing expertise. (Contains 1 table and 4 figures.)