The synthetic nonapeptide DSIP was studied in rabbits and cats under normal conditions and under conditions of disturbed sleep. In other experiments, the effect of the oligopeptide on withdrawal jumping provoked by naloxone in morphine-dependent mice was studied. In rabbits, DSIP at 25 µg·kg–1 i.v. and 1 mg·kg–1 s.c. augmented spindle-dominated, light nonREM sleep and prevented hyposomnia after a stressful situation. In cats, 25 µg·kg–1 i.v. and 100 µg·kg–1 s.c. preferentially augmented REM sleep and abolished the sleep suppressant effect of morphine. In morphine-dependent mice, 25.5 µg·kg–1 i.v. as well as doses beyond 85 µg·kg–1 s.c. attenuated naloxone-induced withdrawal jumping. In most experimental situations, indications for bell-shaped dose-response curves of DSIP were found.