1. The ability of neuropeptide Y (NPY) to modulate skin blood flow, oedema formation and neutrophil accumulation was investigated. Experiments were designed to examine the possible contribution of the Y2 receptor, in addition to the Y1 receptor, through use of Y2 receptor knockout mice (Y2-/-) and selective receptor antagonists. 2. The development of a 99mTc clearance technique for the measurement of microvascular blood flow changes in mouse dorsal skin revealed a dose-dependent ability of picomole amounts of NPY, and also of the Y1-preferred agonist Pro34NPY and the Y2-preferred agonist PYY(3-36) to decrease blood flow. 3. The Y1 receptor antagonist BIBO3304 blocked responses to the Y1 agonist at the lower doses, but only partially inhibited at the higher doses tested in Y2+/+. In Y2-/- receptor mice, the responses to the Y2 agonist were abolished at the lower doses and partially reduced at the highest dose tested, while those to the Y1 agonist were similar in both Y2+/+ and Y2-/-receptor mice. 4. In Y2+/+ receptor mice, the simultaneous injection of the Y2 antagonist BIIE0246 with BIBO3304 abolished Y2 agonist-induced decreases in blood flow over the dose range used (10-100 pmol). When the Y2 receptor antagonist BIIE0246 was given alone, it was not able to significantly affect the PYY(3-36)-induced response, whereas the Y1 receptor antagonist BIBO3304 partially (P<0.001) inhibited the decrease in blood flow evoked by PYY(3-36) at the highest dose. 5. NPY did not mediate either oedema formation, even when investigated in the presence of the vasodilator calcitonin gene-related peptide (CGRP), or neutrophil accumulation in murine skin. 6. We conclude that the major vasoactive activity of NPY in the cutaneous microvasculature is to act in a potent manner to decrease blood flow via Y1 receptors, with evidence for the additional involvement of postjunctional Y2 receptors. Our results do not provide evidence for a potent proinflammatory activity of NPY in the cutaneous microvasculature.