“…Ex periments in several species, including man, have shown that in vivo use of PFC emulsions can produce temporary RES blockade [52]. Moreover, animal experiments have shown that PFC effects on the humoral immune re sponses to immunological 'challenges' are highly variable and dependent on: (1) emulsion composition, (2) dose and route of administration, (3) tissue and species in volved, and (4) timing of emulsion administration rela tive to immune challenge [49,[53][54][55][56], Such variability has inevitably introduced difficulties in assessing the effects of different PFC emulsions on immunological compe tence. The fact that responses are highly species specific also makes it difficult to extrapolate from laboratory ani mals into man.…”