Past studies have claimed that during the Great Migration the church participation of southern black migrants in northern cities was weakened by the circumstances of urban life. The present study, building on theories of subculture formation and the ethnic niche, challenges this claim by examining the participation of blacks in a religious occupation: the ministry. An analysis of Census data suggests that, in those northern cities with relatively large black populations, a “critical mass” of blacks created by in-migration helped to support the entry of blacks into the ministry. The findings are consistent with the assertion that the Great Migration stimulated the church participation of blacks in these cities. They are also in agreement with the argument that the size and distinctive cultural traditions of an ethnic minority group may, together, sustain some of the group's members in a special occupational niche.