Background: The mechanisms underlying cerebral hypercapnic vasodilatation are not fully understood. Objective: To investigate the role of nitric oxide (NO) and ATP-sensitive potassium (KATP) channels in basal blood flow regulation and hypercapnia-induced vasodilatation in rabbit cerebral blood vessels. Methods: The change in cerebral blood flow was measured by a laser Doppler flowmeter in 18 New Zealand white rabbits, in two groups, under general anesthesia with sodium pentobarbital.  N-omega-nitro-L-arginine methyl ester (L-NAME) and glibenclamide were administered locally and systemically before and during induction of hypercapnia. Results: The change in cerebral blood flow was not significant following local and systemic L-NAME administration, showing a non-significant role of local and systemic NO in regulation of rabbit basal cerebral blood flow.  Hypercapnia increased cerebral blood flow by 17.3±4.4% before and 17.3±5.8% after local, and 5.8±3.2% (p<0.05) after systemic L-NAME administration.  The change in cerebral blood flow was not significant after local and systemic administration of glibenclamide indicating a lack of KATP channel role in basal blood flow regulation.  Hypercapnia increased cerebral blood flow by 27.2±8.7% before and 24.7±6.4% after local, and 49.3±9.7% after systemic administration of glibenclamide (p: NS in both cases). Conclusion: Regional NO production had no role in basal cortical blood flow regulation and systemic NO contributed to 66% increment in cerebral blood flow during hypercapnia.  Also, the KATP channels did not mediate the effect of NO or other vasodilators responsible for increasing cerebral blood flow during hypercapnia.