Dissertation (1967): Die Religion der Minahasa Stämme (Nordost-Celebes/Sulawesi), Köln 1968.
Habilitation (1973): Socioeconomic developments and their relations to multidenominational missions in a Benguet community, in: The Cultural Minorities of the Philippines. Philippine Quarterly of Culture and Society, Bd. 2, 1974, S. 61-71.