Serum CPK activity was measured for a total of 33 cases of chronic alcoholics who were admitted to the mental hospital from April, 1975 to January, 1976. The result was examined in relation to the manifestation of the psychotic symptoms in the patients: (1) Twenty six (78.8%) out of 33 cases showed increased serum CPK activity within 48 hours of admission. (2) In most cases that showed abnormal CPK activity, CPK value was the highest at the moment of admission, and then began to fall rapidly, and after one or two weeks settled to the normal CPK level. (3) There was a positive correlation between abnormal CPK activity and the manifestation of the psychotic symptoms in the month before and after entering hospital. In this cases of those having more than 101 IU in serum CPK value, the rate of presenting the psychotic symptoms in a month before or after admission was 90.5% and 71.4%, respectively. The author has given here a report on the above-mentioned results and made some considerations as to pathogenesis of abnormal CPK activity in chronic alcoholism.