Remifentanil is increasingly used in the context of anesthesia, e.g., in patients presenting for MRI examinations, not only as an analgesic but also to replace nitrous oxide. Therefore, a comparative analysis of the effects of commonly used doses of remifentanil and of nitrous oxide on cerebral hemodynamics is warranted. The present study used contrast-enhanced magnetic resonance (MR) perfusion measurement to compare the effects of nitrous oxide (N(2)O/O(2) = 50%; n = 9) and remifentanil (0.1 microg/kg/min; n = 10) on regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV), and regional mean transit time (rMTT) in spontaneously breathing human volunteers. Remifentanil increased rCBF above all in basal ganglia, whereas in supratentorial gray matter the increase in rCBF was equal or even more pronounced when using nitrous oxide. In contrast, nitrous oxide produced a greater increase in rCBV in gray-matter regions than did remifentanil. In summary, nitrous oxide increased rCBV in all gray-matter regions more than did remifentanil. However, the increase in rCBF, especially in basal ganglia, was typically less pronounced than during infusion of remifentanil.