Evidence is reported for the existence and the perceptual relevance of a hitherto rather unattended regularity of melodic patterns in Western music. An inquiry into the occurrence of within-octave melodic intervals in a large variety of examples of Western music showed small intervals to be predominantly descenders and large ones to be ascenders. The perceptual relevance of the distributional regularity in question was tested. Subjects were required to discriminate between computer-generated melodic patterns that were endowed either with the discovered regularity of shape distribution over intervals or with the reversed structure. The results were convincingly positive. Music-theoretical intuitions of Meyer (1956, 1973) are used to account for the data and to claim their generalizability to non-Western melodic patterns. Finally, the outcome of this study is discussed with respect to its relevance to various musicological and music-psychological issues.