In the search for new peptide immunomodulators we asked for thymopoietin and thymopentin-like sequences within the molecules of regulatory and defense proteins. Such an approach appeared to be fruitful in the case of lactoferrin, the protein of TGFβ family, p53 protein, FKBP protein, as well as, of the human leukocyte class II antigen HLA-DQ. The examination of protein sequence data shows that thymopoietin-like motif is very often represented in proteins. It appears, inter alia, in archebacterial histone-like proteins, in histones and in many nucleic acid binding proteins. It suggests that thymopoietin-like motifs originated of the very ancient gene, which coded the nucleic acid binding domain. Some further prospects of utilisation of thymopoietin homology for the research on the field of peptide biological effectors are presented in the paper. The appearance of retrothymopoietin-like sequences within the proteins is also discussed, with the emphasis given to ubiquitin and interferon-γ including factor. The discontinuous thymopoietin-like motifs, appearing in the molecules of G-actin, and heat shock cognate protein HSC70, are also considered. The attempt of the elucidation of the biologically active conformation of thymopoietin on the base of X-ray data given for G-actin is presented.