Secretoneurin (SN) is a neuropeptide derived from secretogranin II that is found in brain and endocrine tissues. The aim of the present study was to determine the influence of this novel peptide on dopamine (DA) release from rat striatum using the microdialysis technique. Rat SN (1–30 µmol/L added to the dialysis buffer) enhanced DA outflow of awake rats in a concentration‐dependent way without marked effects on the outflow of 3,4‐dihydroxyphenylacetic acid or homovanillic acid. The increase in extracellular DA content caused by the peptide was observed throughout the entire period of administration (up to 4 h). Human SN and its 15‐amino‐acid C‐terminal sequence also increased DA outflow, but the effects were smaller than those of rat SN. Two other peptides derived from secretogranin II were without effect on DA efflux. These results establish that SN has a pronounced effect on DA release under in vivo conditions.