Abstract
Among Biomphalaria glabrata/Schistosoma mansoni snail-trematode combinations, it appears that some parasites succeed whilst others fail to infect snails. Snails that become infected are termed susceptible hosts. Those which are not infected are traditionally determined as 'resistant'. Here the concept of B. glabrata resistance to S. mansoni is re-examined in the light of additional observations. It is suggested that, in B. glabrata/S. mansoni, compatibility is tested independently for each individual miracidium and host, and that the success or failure of an infection does not depend on the snail susceptibility/resistance status, but on the 'matched' or 'mismatched' status of the host and parasite phenotypes.