Over recent years there has been an increasing interest in the interaction between Trypanosomatids and in particular the genera Trypanosoma and Leishmania and their vectors. These studies on the "vector parasite interface" have been wide ranging but often suffer from the difficulties of manipulating some of the vector systems. It is now likely that molecular biological and protein analysis techniques can be more effectively applied in dissecting these interactions with a view to identification and characterisation of molecules which control parasite behaviour in vectors. This presentation will review recent studies on Glossina lectins in relation to trypanosome behaviour in flies including recent studies on different G. palpalis subspecies as well as review evidence that trypanosomatids have an effect on their insect hosts for example, on feeding behaviour, susceptibility to insecticides and longevity of infected vectors. Sugars are known to influence development and transmission of Leishmania and recent studies have indicated that aphid/or coccid honeydew is taken by sandflies, the relevance of this to Leishmania/sandfly interactions will be discussed. The basic mechanisms of attachment observed in all trypanosomatid interactions are described and the presence of molecules associated with attachment have been identified. The genetic basis of susceptibility is also becoming better understood and it is to be expected that modern molecular techniques when applied to well defined systems can give results which could permit an attempt at intervention; even if this is not achieved the basic understanding of a widespread phenomenon of the insect/parasite association will have been furthered to permit a better epidemiological knowledge.