Neosporosis is an important cause of pregnancy loss in cattle worldwide. The objective of the present study was to identify Neospora caninum antigens as vaccine candidates using antigen-specific, short-term CD4 T cells established from N. caninum–immunized and –challenged cows. Whole N. caninum tachyzoite lysate was separated into 6 fractions by DEAE anion-exchange chromatography using high-pressure liquid chromatography (HPLC). The CD4 T-cell proliferation assay results indicated that antigenic activity was associated with proteins from HPLC fractions 4–6, with fraction 5 exhibiting the highest antigenic activity. Also, SDS-PAGE analysis revealed a 16-kDa protein in fractions 4–6 that was recognized by anti–N. caninum antibodies. This 16-kDa protein was absent in other fractions, and it may be a target of a T-cell response in cattle. Further identification of immunogenic proteins of N. caninum may facilitate development of subunit vaccines against neosporosis.