The author presents the results of some laboratory experiments carried out to determine the susceptibility of the snail vectors of bilharziasis in Ghana to local strains of Schistosoma haematobium, isolated from children living in two districts near Accra: the Ke district, where Bulinus (Bulinus) truncatus rohlfsi is the important snail vector, and the Pokoasi district, where Bulinus (Physopsis) globosus is the exclusive intermediate host.Each strain was found to be virtually specific in its ability to develop in one or other of the vector species. The "Ke strain" developed readily in B. (B.) truncatus rohlfsi but not in B. (P.) globosus, while the "Pokoasi strain" developed readily in the latter snail but not in the former.The author points out that these findings provide a possible explanation for some of the conflicting observations that have been reported by workers in other African territories, and may have an important bearing on the epidemiology of urinary bilharziasis in Africa as a whole. He stresses the need for further studies on the relationship between bulinid snails and schistosome strains in Africa.