The problem of infection with MPA is virtually limited to pulmonary infection in patients with CF. Conventional vaccine strategies may not be appropriate because the pathogenesis and epidemiology of the infection is so different from the usual acute bacterial infections. MPA strains appear to be suited to long-term parasitism of immune hosts so initial prevention of colonization may be a necessary function of a vaccine. Since infected hosts have antibody to many antigenic components of PA, vaccines which have been used for PA up until now may not have any protective effect for patients with CF. If the switch from NMPA to MPA colonization in vivo is due to the development of host immunity, some vaccines could conceivably promote infection with MPA. A vaccine which produces antibody to the alginate-like mucoid exopolysaccharide might, however, discourage colonization with MPA and studies of this strategy should be promoted.