Spleens from mice immunized with Eimeria bovis sporozoites were removed and the cells fused with mouse myeloma cells to produce hybridoma cell lines (HCLs). The resulting HCLs were examined for antibody (HAB) production against E. bovis sporozoites using an indirect immunofluorescent antibody test on air-dried sporozoites. Four fusions resulted in the production of 19 HCLs that produced HABs to E. bovis sporozoites. These 19 HCLs were further tested for reactivity with cell culture-grown merozoites of E. bovis and Sarcocystis cruzi of cattle; sporozoites of Eimeria tenella from chickens, Eimeria meleagrimitis from turkeys, Eimeria papillata and Eimeria vermiformis from mice; and bradyzoites of S. cruzi from calves. Six HCLs produced HABs that reacted only with E. bovis sporozoites and were species specific/stage specific. Two HCLs produced HABs that reacted only with E. bovis sporozoites and merozoites, and were species specific/stage cross-reactive. Seven HCLs produced HABs that reacted with the sporozoites of the other Eimeria species examined and were species cross-reactive/stage specific. Four of the HCLs produced HABs that reacted with all organisms tested and were species cross-reactive/stage cross-reactive. The results of this study suggest the conservation of some antigens throughout developmental stages and genera of Eimeriorina.