There is little doubt that the use of insecticide treated bed nets (ITN's) is one of the most successful means of reducing malaria in Africa. However, vectors in this region tend to be late night, indoor feeders. Vector species in other parts of the world may not be so susceptible to this form of vector control. In much of Central & Southern America, the major vectors such as An. darlingi and An. albitarsis have a feeding peak between 8 - 10pm, before most people retire to bed. Similarly, the major vector in much of S.E. Asia, An. dirus, seldom enters homes to feed. In these circumstances it is unlikely ITN's alone will provide adequate protection. Supplemental use of skin applied insect repellents may be an effective method of personal protection in the hours between dusk and retiring to bed. It would also prove useful for those individuals working late or moving early into the forest where exophagic species are encountered. As yet, there have been no robust clinical evaluations of combined ITN and repellent use. This double blind, placebo-controlled study is designed to evaluate the efficacy of combined ITN and plant based insect repellent use to reduce P. falciparum in the Bolivian Amazon in a region where ITN's alone are likely to be ineffective.