Four chimeric synthetic peptides (Q5, Q6, Q7(circle times), and Q8(circle times)), incorporating immunodominant epitopes of the core p19 (105-124 a.a.) and envelope gp46 proteins (175-205 a.a.),, of HTLV-I were obtained. Also, two gp46 monomeric peptides M4 and M5(circle times) (Ser at position 192) were synthesized. The analysis of the influence of the peptide lengths and the proline to serine substitution on the chimeric and monomeric peptides' antigenicity, with regard to the chimeric peptides Ql, Q2, Q3(circle times), and Q4(circle times), reported previously, for HTLV-I was carried out. The peptides' antigenicity was evaluated in an ultramicroenzyme-linked immunosorbent assay (UMELISA) using sera of HTLV-I/II. The peptides' antigenicity was affected appreciably by the change of the peptide length and amino acid substitutions into the immunodominant sequence of gp46 peptide. (c) 2005 Elsevier Inc. All rights reserved.