The invention is related to the field of biotechnology, in particular, to synthetic peptides having immuno-stimulating properties, and can be used in medicine. A series of peptides has been synthesized that differ in their chemical structure from prior art biologically active Alloferon and Allostatin peptides. The distinction is that position 6 of the structure His-Gly-Val-Ser-Gly-X-Gly-Gln-His-Gly-Val-His-Gly, instead of histidine or tryptophan characteristic of those peptides, is occupied by other amino acids of aliphatic and aromatic series or by their chemical modifications. The peptides obtained are used as a part of an immunomodulatory and antiviral pharmaceutical composition. The invention makes it possible to obtain peptides that induce efficiently production of interleukin-18 and interferon gamma.