Effects of intracerebroventricular (ICV), neuropeptide Y (NPY) (0.2-5.0 nmol) and its C-terminal 13-36 amino acid (AA) fragment (0.4-2.0 nmol) have been examined with respect to anxiolytic properties in two rat anxiety models, Montgomery's conflict test (MT), and Vogel's drinking conflict test (VT). In the MT, 1.0 and 5.0 nmol NPY abolished the normal preference for the closed arms of the maze. At 5.0 nmol, the total number of entries made into both closed and open arms was decreased by 50%. In the VT, both 0.2 and 1.0 nmol NPY markedly increased the number of shocks accepted. The effect of 5.0 nmol NPY was less pronounced. In control experiments, NPY (0.2 nmol) did not affect pain sensitivity or thirst. Pretreatment with the selective alpha 2-adrenergic receptor antagonist idazoxan, at a dose which by itself did not affect behaviour (2.0 mg/kg), antagonized the effect of 1.0 nmol NPY in the VT. NPY 13-36 was without significant effect in both models. The results suggest that NPY exerts anxiolytic-like effects, and that these effects are mediated through an interaction with noradrenergic systems. Higher doses of NPY produce sedation and ataxia, which decrease overall activity in the MT, and interfere with the ability fully to express behaviourally the anxiolytic-like effect in the VT. The findings are discussed in relation to the noradrenaline hypothesis of anxiety, and to observations indicating involvement of NPY in the pathophysiology of major depression.