Research on bonamiasis, an epizootic disease of the edible oyster Ostrea edu/is caused by the protozoan Bonamia ostreae, is discussed in relation to oyster fanning, research technology, epizootiology, and management. Morphological and infectious characteristics of the parasite are described. Recent progress in isolation and purification of the parasite have permitted investigations into host defense mechanisms, parasite infectivity, and the development of a mol1usc-pathogen mode!.