• Serum creatine phosphokinase (CPK) activity was determined in a series of 101 sequential admissions to the Pritzker Children's Hospital, an inpatient psychiatric facility. Black children had significantly higher serum CPK levels than whites, and males had significantly higher levels than females, as is the case with adults. There was a higher incidence of CPK elevations in children with organic brain pathology than in children with personality disorders or schizophrenia. Children with chronic symptoms of a psychotic nature did not have increased serum CPK activity, which is similar to the findings in adults. There were no children in the sample with acute psychotic symptoms, so it was not possible to determine whether acute psychosis in children is accompanied by increased serum CPK activity, as it frequently is in psychotics over the age of 17.