Studies on the autoregressive powerspectrum of EEG and its component analysis were carried out by using minicomputer PDP 11/40 (DEC) in 37 cases with cyclic vomiting who showed no spikes in EEG during the attacks and the reconvalescent stages. The records of 37 cases during the attacks and of 15 cases during the free intervals were obtained from scalp electrodes at monopolar PF₁, PF₂, C₃, C₄, O₁ and O₂ regions according to the “10-20” international system during the awaking period. The data were recorded on the analog tapes as well as the paper sheets. The 20 second artifact free segment of records was digitalized at 50 samples/sec. and the natural frequency, the damping coefficient, the damping time, the time consant and the mutual information amount of component were calculated by the method of autoregressive analysis (Sato and Ono, 1975, 1976.). The reults were summerized as follows:<BR>1.37 records of EEG during the attack stages were decomposed into 168 components and 15 records during the reconvalescent stages were into 63 components.These components consist of the second order oscillatory activities of alpha, delta, theta and beta rhythms and of the first order nonoscillatory activities of delea (δ₀) wave.<BR>2. The second order activity was a damping oscillatory process characterized by the frequency of oscillation and the damping coefficient (ρ). The damping coefficinet of theta and beta waves were more decreased during the attack than during the reconvalescnet stages. These results imply that the damping oscillaion of theta and beta waves were longer in duration during the attacks than during the reconvalescent stages.<BR>3. The percentages of the powers of delta and beta waves were higher during the reconvale scent than during the attack stages, whereas that of theta wave showed a significantly higher value during the attack stages.<BR>4. The mutual infomation amounts of delta and beta waves showed sigificantly higher values during the attacks, while that of theta wave was higher during the reconvalescent stages.<BR>5. From the results described above, it was suggesed that the decreased damping coefficient of theta wave during the attack stages would bedue to the inhibition to the subcortical (thalamic) rhythmical pacemaker mechanism.