For the purpose to study the effect of various nucleic acid derivatives on the blood flow, oxygen consumption, glucose uptake, output of lactic acid, and EEG of the perfused brain, perfusion experiments were conducted by a modified method of Geiger & Magnes with non-anesthetized cats made immobile with d-tubocurarine. Nucleic acid derivatives used in the experiments were Adenosine, ATP, AMP, Guanosine, GMP, Cytidine, CMP and UMP. Each of these was injected rapidly into the carotid artery of the perfusing brain. In addition, for the continuous effects of ATP, UMP and CMP, artifcial blood containing these nucleotides was perfused. The results of the study are briefly presented as followed. 1) As for the accelerating effect of these nucleic acid derivatives on the blood flow, Adenosine and Guanosine, nucleosides of the purine derivatives and ATP, AMP and GMP (nucleosides of the san e derivatives) all showed the accelerating effect, but ATP had the strongest effect and AMP as well as Adenosine showed about an equal but slightly weaker effect than that of ATP. GMP and Guanosine did not show much accelerating effect on the cerebral blood flow. 2) The accelerating effect of ATP on the cerebral blood flow was transient lasting only for a short time. This seems to be due to the lowered vascular resistance by direct dilatating action of this substance on the blood vessels. In contrast, the accelerating effect of Adenosine, while it was somewhat weaker than that of ATP, was rapid and lasted several times longer than that of ATP. 3) In the case of perfused brain given rapid ATP injection, irrespective of the dose of ATP, simultaneous with the increase of the cerebral blood flow there occurred an increase in oxygen consumption, glucose uptake and lactic acid output of the brain, while such an increase was not so marked in the cases injected with AMP, Adenosine, GMP and Guanosine. 4) Cytidine (nucleoside of the pyrimidine derivatives) and CMP, UMP (nucleotides of the same derivatives) had hardly any effect on the blood flow and oxygen consumption of the brain, but these substances increased glucose uptake and decreased lactic acid output. 5) A rapid injection of these nucleic acid derivatives hardly affected EEG of the perfused cat brain, but when the brain perfusion was carried out continuously with artificial blood containing CMP and UMP, the glucose uptake was increased and lactic acid output decreased also the fuctional level of the perfused brain was well maintained throughout the perfusion experiment for more than one hour.