Antigenic variation in trypanosomes has been the subject of several recent and comprehensive reviews. The substance of my own contribution to reviewing current highlights of this topic is being published elsewhere. In the absence of new results to comment upon, I shall in the present report restrict myself to a concise summary of the structure and possible functions of the major variant surface antigens of Trypanosoma brucei, concluding with a brief assessment of the prospects for immunoprophylaxis and improved diagnosis of the African trypanosomiases in the light of an increased understanding of antigenic variation. It is now clear that antigenic variation in T. brucei can be largely, if not entirely, explained by the sequential expression of alternative cell surface glycoproteins. It seems likely that similar groups of glycoproteins are responsible for antigenic variation in other salivarian trypanosome species. The repertoire of alternative antigens which may be expressed by a trypanosome clone, strain or species, or with a certain geographical area, is so far undetermined but may run to several hundred.