DSIP — delta sleep-inducing peptide — is a nine-amino-acid chain first isolated in 1977 from the cerebral venous blood of rabbits by a Swiss group studying how sleep states transfer between animals. Its name comes from the delta-wave, slow-wave sleep it was associated with in that original work, and it has since been detected in human tissue and fluids. Half a century on it remains a research peptide with an unsettled mechanism, commonly researched for its part in sleep architecture, in the stress response and in the endocrine rhythms that run alongside sleep. Supplied as 5mg of freeze-dried powder per vial, for reconstitution with bacteriostatic water; store at 2–8°C.