The filarial worm Brugia pahangi and the mosquito Aedes aegypti were used as a model system to study the interrelationship between migrating infective larvae and the vector. The distribution of parasites within the host population was shown to be over-dispersed and could be described by a negative binomial distribution. The degree of overdispersion and mean parasite burden progressively declined during the course of infection. The decline in mean parasite burden was attributed to density-dependent parasite-induced host mortality as well as to the direct loss of infective larvae from the mosquitoes. The course of larval migration within the mosquito was described and the evidence suggested that migration may occur solely due to "non-directional" translatory movement by the larvae. The effects of larval migration on the spontaneous flight activity and survival of infected mosquitoes were shown to be detrimental. Transmission of larvae during blood-feeding often resulted in abnormal feeding behaviour and an increased mortality of infected mosquitoes. Humidity, temperature and the nature of the skin surface upon which the infective mosquitoes fed were shown to effect the efficiency of filarial transmission.