ABSTRACT: Eosinophils were quantitated in sections of luteal tissue obtained from sheep treated with a luteolytic dose of prostaglandin (PG) F2α. Increased numbers of cells were detected before the onset of either functional (decline in sera or tissue concentrations of progesterone) or morphological regression. Luteal tissue was shown to produce a specific chemoattractant for eosinophils as assessed by a linear under-agarose migration assay. Eosinophils were responsive toward leukotriene B4, but not toward PGF2α or a synthetic N-formyl peptide. Because eosinophils are capable of mediating tissue damage in immune/inflammatory conditions, it is suggested that these cells could play a similar role in the mechanics of luteolysis.