Citric acid conecnetrations in sera and cerebrospinal fluids of various psychotic patients and of normal persons were determined by Natelson's method; and the following results were obtained. Citric acid concentrations in serum: In comparing the citric acid concentrations in sera of various types of schizophrenic patients with that in serum of normal persons, it has been found that in hebephrenic form it is lower than in the normal, while in catatonic form it ranges widely from higher to lower, and in paranoid form it is nearly the same as that in the normal. In depressive form it tends to be lower than that in the normal. A marked decrease in the concentration has been observed both in chronic and deteriorated schizophrenia as well as in stupor, whereas a marked increase can be recognized in excited state. Citric acid concentration in cerebrospinal fluid: Citric acid concentration in cerebrospinal fluid has been found to be 2 or 3 times that in serum; and the value in the cerebrospinal fluid of lumbar region is greater than that in cerbral region. The concentration in the cases such as cerebrovascular disease and postlobotomy cases show an increase, whereas in hydroce-phalus it is slightly lower.