Single application of glycine in a final dose of 40 mg/kg to the surface of the parietal area of rat brain produced a potent vasodilatory effect. The diameter of arterioles increased to 250% from the baseline level 1-3 min after treatment. These changes persisted for 5-10 min. In the follow-up period the diameter of vessels progressively decreased to the baseline level. Repeated application of glycine in the same dose also induced dilation of arterioles. Application of physiological saline under similar conditions did not produce these changes.