The behavioral effects of intracerebroventricularly administered neurotensin (NT), some NT fragments and two synthetic NT analogs were investigated in the open field. Each peptide was studied in both a 'novel' (no pre-exposure) and a 'familiar' (with pre-exposure) environmental situation. Neurotensin decreases locomotor activity in the periphery but increases the time spent in the central area of the apparatus. Of the congeners tested, D-Phe11-NT has similar effects to NT whereas the NT fragments were generally inactive. These findings indicate that the intact peptide or stable substituted NT analogs, but not small C- and N-terminal fragments of NT, are behaviorally active after intraventricular administration.