Abstract: 13 cell lines of hybrids secreting monoclonal antibodies (McAb) against erythrocytic stages of P. yoelii were established by fusing Sp 2/0 myeloma cells with spleen cells of BALB/c mice immunized with crude preparation of merozoil.es of the same malaria para- sue. me 13 McAbs ootamea can be classified according to IFA results into 4 groups: 1. against various developmental forms of P. yoelii in erythrocytes; 2. against late tro-phozoites and schizonts; 3. against schizonls and jnerozoites- and 4. against merozoites only. Five of the 13 McAbs showed cross immunofluorescence with human malaria parasites, in which 4 crossed with P, falciparum only.and 1 crossed with both P. falcipa-rum and P. vivax. It indicates that there are common antigens not only between rodent and human malaria parasites, but also between P. falciparum and P. vivax. The distri-; bution and quantity of the common antigens between different species of malaria parasite are not always the same. These differences should be carefully considered when hetero-genous malaria parasites are used for immunodiagnosis or for vaccination experiments. Immunofluorescence could not be observed on the surface of infected RBC when fresh infected RBC were used as target cells in indirect IFA test with McAbs.