Adults (n = 28) and 8-month-old infants (n = 48) listened to repeated transpositions of a 10-note melody exemplifying the rules of Western tonal music. They were tested for their detection of two types of changes to that melody: (a) a 4-semitone change in 1 note that remained within the key and implied dominant harmony (diatonic change) or (b) a 1-semitone change in the same note that went outside the key (nondiatonic change). Adults easily detected the nondiatonic change but had difficulty with the diatonic change. Infants detected both changes equally well, performing better than adults in some circumstances. These findings imply that there are qualitative differences in infants' and adults' processing of musical information.