Taenia solium and Taenia saginata are of such close taxonomic relationship that each can be regarded as a model for the other. In these particular species the only available hosts are either humans or large domesticated animals. This has imposed severe safety and/or economic restrictions on the extent of the experimental work which could be attempted. Furthermore, there is a limit to the relevance of work with less closely related species such as Taenia ovis, Taenia taeniaeformis and Taenia pisiformis with their differing host species, larval forms and locations within the intermediate host tissue. However, the application of both monoclonal antibody based and modern molecular biological techniques to the T. solium and T. saginata systems does much to overcome or circumvent some of the problems. Thus advances made in the analysis, diagnosis or immuno-prophylaxis of one of these species are at least potentially both of direct and immediate or indirect benefit to the work on the other species.