expressing the 3 39 and 5 39 repeats of resa these proteins were tested for immunogenicity by immunizing rabbits with 0 25 0 5 mg amounts of antigen together with complete freund 39 s adjuvant the rabbits were boosted with similar amounts of antigen in incomplete adjuvant 4 6 weeks later in each case antibodies were elicited which reacted with the resa molecule expressed in p falciparum growing in vitro three resa synthetic peptides table 1 conjugated to keyhole limpet haemocyanin were used to immunize mice and the resulting antisera were assayed against each of the three peptides conjugated to bovine serum albumin and against fused polypeptides corresponding to the 3 39 and 5 39 repeats of resa and sonicates of infected erythrocytes all mice immunized with these peptides produced antibodies that were reactive with the homologous peptide and the fused polypeptide containing that sequence in addition peptide resa 3 39 2 eenv x4 induced antibodies that also reacted with the other 3 39 repeat peptide resa 3 39 1 eenvehda which has a 5 amino acid sequence in common the reverse however was not true anti resa 3 39 1 antibodies did not react with resa 3 39 2 when these anti peptide antisera were assayed on peptide bsa conjugates there was no apparent cross reactivity between the 5 39 and 3 39 repeats of resa however assaying the same sera on fused polypeptides revealed that the peptides had induced antibodies that reacted with both repeat structures although the reaction with the heterologous repeat was very weak in comparison to that with the homologous repeat the anti peptide antisera were used to probe western blots of infected erythrocytes all of the antisera reacted specifically with the mr 155 000 resa polypeptide table 1______________________________________sequences and synthetic peptides corresponding torepeats in.