Although infection prevalence and intensity increased with temperature and salinity in P. marinus-challenged oysters of both oyster species, they were highest in C. virginica groups. Infection intensity was significantly higher in P. marinus-challenged C. virginica than C. gigas at all temperatures; however, infection prevalence was not satistically different at any temperature treatment. In all salinity treatments, prevalence and infection intensity were significantly higher in P. marinus-challenged C. virginica than C. gigas.