 One of the greatest challenges to those planning vector control programmes in developing Countries is the provision of cover to those populations in remote or isolated areas. Commonly, it is these communities which bear the greatest burden of disease due to location and inaccessibility to local health care. Yunnan Province is a good example of such problems. The border region with Laos, Myanmar and Vietnam contributes a high proportion of all malaria cases in the whole of China, yet few if any disease control initiatives cover the rural minority peoples and migrant workers who inhabit the region. Comprehensive ethnobotanical surveys in the area have shown many of the 25 minority peoples living in isolated communities already use traditional herbal forms of mosquito control utilising several of the abundant species in the particularly diverse local environment. Having identified a number of potentially useful plant species being used, in terms of their availability, sustainability, low cost free and known chemical constituents, the investigators and the local Chinese malaria control officials consider a phase II evaluation of the most promising candidates is justified. In particular, 4 widely used plants are traditionally used as fumigants to reduce prevent mosquitoes entering houses, either by burning dried or fresh material on the indoor cooking fires each evening, or by spraying tinctures around entry sites like eaves windows. Due to the method of use, it would be very difficult to simulate this in the laboratory, so a simple means of field evaluation has been chosen. 