This paper deals with the development of ethnology in Slovakia from 1945 to 1950. To a lesser extent it tracks the penetration into this scholarly discipline of Marxism, in the context of its promotion by the governing regime after the communist seizure of power in 1948. More detailed attention is given to the penetration of the Soviet ethnographic school, founded on historical and dialectical materialism, into the ethnology during this period. The first section of the paper contains a detailed characterisation of the Ethnological Institute of the Slovak Academy of Sciences and Arts (1946-1953). In the second section the paper offers information on the fieldwork activity which the Ethnological Institute carried out during 1950 in the vicinity of the town Modry Kamen, in the south-central part of Slovakia. The reconstructed fieldwork is analysed as an instance of the penetration of communist ideology into a discipline in the totalitarian system. The reason why the research project in the Modry Kamen region is taken as a model example is the fact that scholars in the Ethnological Institute, in the time between the project's preparation and the publication of its results, began a programmatic orientation of ethnology on the theoretical and methodological planes towards Marxism.