Humanin (HN) is a newly discovered 24-amino acid peptide, which may suppress neuronal cell death. HN cDNA includes the open reading frame (HN-ORF) of 75 bases, located 950 bases downstream of the 5' end of the HN cDNA. It was demonstrated that HN cDNA is 99% identical with mitochondrial DNA (mtDNA) sequence. HN homologues have been identified as expressed sequence tags (ESTs) in rat and nematode. Certain regions homologous to the HN cDNA exist on human chromosomes. HN forms homodimers and multimers and this seems to be essential for the peptide functions. HN acts as a ligand for formyl peptide receptor-like 1 (FPRL1) and 2 (FPRL2). It was demonstrated that HN plays a protective role by an antiapoptotic activity interfering with Bax activation, and suppressing Bax-dependent apoptosis. HN is also shown to suppress the c-Jun N-terminal kinase (JNK) and ASK/JNK-mediated neuronal cell death. Several studies also confirm that HN could be important in prevention of angiopathy-associated Alzheimer's disease dementia, diseases related to mitochondrial dysfunction (MELAS), and other types of beta-amyloid accumulation associated neurodegeneration. A very recent study demonstrated a pluripotent cytoprotective effect and mechanisms of HNs in cells other than from the CNS, such as germ cells, or panreatic b-cells, and potent physiological consequences that result from HN interaction with IGFBP3 and STAT3. The in vivo studies suggest that humanin may protect against cognitive impairment, also due to ischemia/reperfusion injury.