Two malaria surveys in the central mountains of Netherlands New Guinea are described, one of which was carried out during an epidemic. In the Baliemvalley A. farauti and A. koliensis were collected; in the Kemaboevalley larvae of A. koliensis. These anophelines are well known vectors, though their role in transmission could not be proved in the areas concerned. The epidemiological importance of trader-tribes and of a salt well for the spread of the disease in the highlands is stressed. It is suggested that the borderline of transmission in New Guinea is situated below 1,700 m. The possibility that the exophilic habits and a relatively short average duration of life of the anophelines might be an impediment for the spread of malaria to higher altitudes, is discussed.