Creatine kinase (CK) is responsible for the creatine/creatine phosphate level which that is known to alter in the brain of patients with schizophrenia. A comparative estimation of CK enzymatic activity and immunoreactivity of CK BB was carried out in readily soluble extracts from frontal cortex, anterior and posterior cingulate cortex, hippocampus and cerebellum from brains of individuals with schizophrenia versus normal controls. CK activity was determined using a commercial diagnostic kit. CK BB immunoreactivity was evaluated by ECL -immunoblotting using monoclonal antibody. A drastic drop of CK activity and CK BB immunoreactivity was observed in all the examined brain areas in schizophrenia patients compared to controls (p<0.01), with the maximum drop in the cerebellum. The reduction was independent of age, postmortem interval or chlorpromazine equivalent. The decreased level of CK BB in schizophrenia was confirmed by purification of CK BB from brains of patients with schizophrenia and control brains: the yield of the purified enzyme was significantly lower in schizophrenia, wherein molecular masses of CK B-subunits were equal. Possible causes and consequences of the decrease in CK BB level observed in brain of patients with schizophrenia are discussed.