The autoregressive analysis of the “ eyes-closing reaction ” (Fukuyama) of EEG in cyclic vomiting was studied in 7 cases of patients (4 boys and 3 girls), 5-7 year of age, with the eyes closed and open during the attack and at the reconvalescent stages.The EEG were recorded from scalp electrodes at PF ₁, PF ₂, C ₃, C ₄, 0 ₁ and 0 ₂ regions according to the “ 10-20 ” international system.<BR>The records were stored on the analog tape during the 10 seconds period of rest with the eyes closed and then for 70 seconds continuously with the eyes open.Each 10 second artifact free epoch of record was digitized at 50 samples/sec.and the natural frequency, the damping coefficient, the damping time, the time constant and the mutual information amount of component with the eyes closed and open were calculated by the method of autoregressive analysis (Sato and Ono, 1975, 1976) with a minicomputer PDP 11/40 (DEC).The results were summerized as follows:<BR>1) The mean frequency of the frontal beta and the central theta rhythms shifted to the 1 Hz lower frequency with the eyes open during the attack than during the reconvalescent stage.<BR>2) The mean percentage of powerintensity of alpha activity to that of the high order activity was significantly more decreased at the occipital region, while that of delta and theta activities at the frontal and the central regions were significantly more increased with the eyes open during the attack than during the reconvalescent stage.<BR>3) The duration of oscillatory process of the frontal alpha and theta rhythms was significantly shorter with the eyes open during the reconvalescent stage.On the other hand, the longer duration of beta rhythm and the shorter duration of delta rhythm with the eyes open were observed during the attack stage.<BR>4) During the period of rest with the eyes open, the mutual information amount of alpha and theta rhythms was reduced during the reconvalescent, whereas that of delta rhythm decreased during the attack stage.<BR>5) According to Freeman's hypothesis“ K-Set of neural mass action ” (1975), the first order autoregressive activity of nonoscillatory process may be given as KO, KI-Sets and the second order activity of oscillatory process as a KII-Set.Therefore, it was speculated that the “eyesclosing reaction ” (Fukuyama) of EEG in cyclic vomiting might involve the selective decrease of KO, KISets in neural mass action.