Studies of some vector-borne diseases have shown genetic factors to be involved in the vector–parasite relationships and these results have often influenced measures taken to control such diseases. Novel methods of vector control have emerged from genetical studies, such methods having the dual advantages of being species specific and of causing little environmental damage. However, genetics has made little impact on trypanosomiasis research or control when compared with other vector-borne diseases, for reasons which are related to the biology of the tsetse fly and the trypanosome. Despite these natural limitations, genetical studies may yet provide useful information for those engaged in trypanosomiasis research. For example, chromosome and isozyme studies have shown that there is a large amount of genetic variation within tsetse populations, but it is not known whether such variation is related to the distribution of the disease. The infection rates of flies are known to vary between species and are dependent on fly-trypanosome interactions but it is not known whether these interactions have a genetic component. It is suggested that studies of the genetics of natural populations of tsetse, combined with selection experiments in the laboratory, could provide answers to these questions which might be of importance to control programmes and to studies of the epidemiology of trypanosomiasis.