The factors responsible for eosinophil recruitment are poorly defined, although both platelet-activating factor (PAF) and cytokines appear to be involved in regulating this process. We compared eosinophil mobilization induced by PAF or antigen injection in the peritoneal cavity of hypereosinophilic rats and the effects of the PAF antagonist BN 52021, the somatostatin analog BIM 23014, and cyclosporin A on this process. PAF induced a significant increase of both peritoneal and circulating eosinophil count. Cyclosporin A almost totally abrogated these variations, whereas BN 52021 reduced the peritoneal increase. Similarly to PAF, peritoneal antigen challenge in actively sensitized animals increased peritoneal and circulating eosinophil counts. Cyclosporin A abolished both hypereosinophilia and peritoneal eosinophil infiltration. BIM 23014 reduced the circulating eosinophils and cell infiltration. In contrast, BN 52021 primarily decreased peritoneal eosinophil recruitment, while having little effect on circulating cells. The different mechanisms of action of these drugs and the involvement of interleukin 5 in eosinophil recruitment are discussed.