Sense peptides are coded for by the nucleotide sequence (read 5'-->3') of the sense (positive) strand of DNA. Conversely, a complementary peptide is coded for by the nucleotide sequence (read 5'-->3') of the complementary or antisense (negative) strand of DNA. In many instances, sense and corresponding complementary peptides have been observed to interact specifically. In order to study this process in more detail, longer, shorter and mutant variants of our original complementary peptide, VITFFSL, were synthesised and analysed for binding to and inhibition of cytokine human interleukin-1beta (IL- 1beta) in vitro. The behaviour of all peptides studied is discussed in terms of the Mekler- dlis (M-1) pair theory, a theory that accounts for specific sense-complementary peptide interactions in terms of through-space interactions between corresponding pairs of amino acid residues (M-1 pairs)] specified by the genetic code and its complement.