A γZap II cDNA expression library, constructed from Eimeria acervulina (PAPa46 strain) sporulated oocyst stage, was screened with sera raised to E. acervulina or Eimeria tenella oocysts in order to isolate clones coding for antigens common to the two species. Most of the clones isolated were derived from the same gene. Antisera raised to a recombinant glutathione-S-transferase fusion protein IP reacted with an antigen of 19 kDa in immunoblot of E. acervulina sporulated and unsporulated oocysts. Immunofluorescence of E. acervulina sporozoites indicated that the antigen is located in the cytoplasm. The anti-1P antisera reacted on immunoblots of E. tenella with a 19-kDa antigen and by immunofluorescence on E. tenella, Eimeria maxima and Eimeria falciformis sporozoites, indicating that the antigen is conserved in Eimeria species. DNA sequencing indicated that the sequence was almost identical to that of clone cSZ1 previously described by Jenkins et al. [1] using E. acervulina strain #12. The 1P insert hybridized to a 1150-nt mRNA from E. acervulina PAPa46 strain and strain #12, a size consistent with the observed molecular weight of the protein.