We have examined the hypothesis that cytokines mediate the enhanced responsiveness of eosinophils to PAF in sensitized mouse skin. PAF (10 ng per site) resulted in a considerable degree of eosinophil accumulation in ovalbumin (OA)-sensitized mice but not in non-sensitized mice. Intradermal preadministration of cytokines (IL-5, IL-3 and GM-CSF) also significantly enhanced PAF-induced migration of eosinophils in a dose-dependent manner. The relative potency with which these cytokines primed cell migration was IL-5 greater than IL-3 greater than GM-CSF, however, each cytokine alone showed no direct effect. We conclude that the sensitization or the exogenous application of cytokines is capable of augmenting PAF-induced eosinophil migration in mice in vivo, and the cytokines thus elicited by sensitization may contribute to the extensive recruitment of inflammatory cells in allergic diseases.