Under the current epidemiological conditions as found in Korea, and considering the limited funds available for the malaria project, passive case detection proved to be the only practical mechanism to obtain reliable data required for the delimitation of malarious areas. The malaria map of the country was completed at the end of 1965. The high SPRs found among the blood smears reported by the PCD undts are due to the fact that the Korean farmer is able to recognize the clinical symptoms of the disease. The "fever case" reports are therefore actually "suspect malaria case" reports. The consistently high SPR has resulted in the detection of a large number of parasite carriers with the number of smears to be examined being reduced to a minimum. Although the medical group gave an important contribution to the success of the PCD service in Korea, the number of medical and public health facilities in the rural areas are still too small. This made it necessary to obtain the collaboration of laymen groups like school teachers, village chiefs etc., and their participation largely contributed to the success of the present programme. The degree of collaboration by the PCD units is higher in the more malarious areas. As no form of encouragement e.g., a reporting fee, has been given to these laymen during the past few years it becomes increasingly more difficult to maintain their active co-operation. It is felt that through passive case detection alone it will not be possible to collect adequate information to provide the proof for the complete interruption of transmission.