The peptide bioregulator research programme developed in Soviet and Russian science from the 1970s onwards produced a family of short peptides proposed to exert organ-specific regulatory effects. Two of the most studied — Epithalon (pineal-derived tetrapeptide) and Thymalin (thymic extract) — have points of intersection with growth hormone axis biology that make them relevant to HGH research, even though they are not GH secretagogues themselves.