This study showed that the antigenicity of a malarial epitope increased with the length of the epitope when inserted at positions aa 2 6 (amino acid position 26) and aa 1 9 6 , but not at aa 2 1 3 , of the Pseudomonas aeruginosa major outer membrane protein OprF (326 amino acids). Immunization studies showed that a 19-aa epitope was significantly more immunogenic than a 7-aa epitope when inserted at aa 2 6 of OprF, while neither an 11- nor a 19-aa epitope fused to the C-terminus of glutathione S-transferase was immunogenic.