Quantification of mucosal eosinophils and mast cells in the oviducts from 22 crossbred heifers was performed in both natural (estrus, metaestrus and diestrus) and superovulated (estrus and metaestrus) estrous cycles. The number of cells/square millimeter of mucosa was obtained through counts at different regions of the oviduct (infundibulum, ampulla, ampullary/isthmic transition and isthmus). Differences were not found (P > 0.05) among numbers of cells at the different phases of the natural estrous cycle nor between natural or superovulated cycles. When all animals were separated into two phases of the estrous cycle (estrus and metaestrus), the number of eosinophils at the ampullary/isthmic transition and isthmus was higher (P < 0.01) at the estrus cycle phase, and the number at the infundibulum was higher (P < 0.001) during the metaestrus phase than at estrus. The number of mast cells was highest at the isthmus regardless of the estrus phase, and highest at the infundibulum (P < 0.001) and ampulla (P < 0.05) during the metaestrus phase. Significant correlations were found between the number of mast cells and plasma progesterone levels at the infundibulum (P < 0.001; r = 0.69) and ampulla (P < 0.03; r = 0.51). No correlation was seen between numbers of eosinophils and mast cells, progesterone and 17β-estradiol concentrations. Therefore, the distribution of mucosal eosinophils in the oviduct of heifers is apparently not related to the circulating levels of 17β- estradiol and progesterone; however, the highest number of mast cells found at the metaestrus phase of the cycle, at least for the infundibulum and ampulla, appears to be related to the high circulating progesterone plasma levels in metaestrus phase compared to estrus phase. No differences were found between animals subjected or not to superovulation