Aside from Don Randel's study of the responsory verse tones, there have been few comparative analyses of Old Hispanic chant melodies. Such comparison requires new methods because of the paucity of surviving manuscripts, the limited sharing of repertoire between them and the nature of the notation. This article examines variants in specific opening and cadential contexts, across the Old Hispanic corpus. In these contexts, cantors chose from a system of interchangeable melodic shapes, which vary by manuscript. Some manuscripts cluster in their choices of these shapes, in ways that confirm Randel's findings, with four melodic dialects in evidence (‘Leon’, ‘Rioja’, ‘Toledo A’ and ‘Toledo B’). Other manuscripts, however, do not fit securely into any of these four dialects, instead showing a certain degree of permeability between the dialects. Although the types of variants we have identified, including differences in notation and melody, may appear ‘insignificant’ in comparisons of individual chants, they emerge as significant markers of melodic dialects in comparisons of large data sets.