Rainbow trout, immunized by the immersion method against Vihrio unguillurum. were used as donors of plasma and celis for transfer to unimmunized trout. Recipients were then challenged with a 20 min exposure to a virulent Vibrio unguillurum suspension, and the mortality was compared to that of trout receiving plasma and cells from unimmunized donors. Immunity was successfully conferred by plasma taken from immune donors 16 days post-immunization (PI), and by pronephros and spleen cells from Day 20 and 21 PI donors. Plasma was most effective in transferring vibriosis protection, followed by pronephros cells. Splenocytes gave variable results, while trials with thymus cells were negative in all cases.