This Article Reports Two Experiments. In the first experiment, 13 professional singers performed a vocal exercise consisting of three ascending and descending melodic intervals: minor second, tritone, and perfect fifth. Seconds were sung more narrowly but fifths more widely in both directions, as compared to their equally tempered counterparts. In the second experiment, intonation accuracy in performances recorded from the first experiment was evaluated in a listening test. Tritones and fifths were more frequently classified as out of tune than seconds. Good correspondence was found between interval tuning and the listeners responses. The performers themselves evaluated their performance almost randomly in the immediate post-performance situation but acted comparably to the independent group after listening to their own recording. The data suggest that melodic intervals may be, on an average, 20 to 25 cents out of tune and still be estimated as correctly tuned by expert listeners.