A 17-year-old man developed the malignant neuroleptic syndrome and recovered after the neuroleptic drug was discontinued. When the treatment with the neuroleptic was resumed four weeks later, an elevated serum creatine kinase level was found without any other symptoms of the malignant neuroleptic syndrome. The neuroleptic was discontinued and the serum creatine kinase level was normalized. In both episodes, serum creatine kinase level was followed daily. The elimination of creatine kinase followed a first order kinetic, indicating that release of the enzyme to the blood stopped as soon the neuroleptic was discontinued. In the second episode, the increase in serum creatine kinase level was found before the symptoms of malignant neuroleptic syndrome appeared. This opens a possible way to early diagnosis and in that way prevention of severe symptoms.