Various laboratory tests have been used to predict the survival of patients with amyotrophic lateral sclerosis (ALS). The serum creatine kinase (CK) level is frequently elevated in patients with ALS. This study evaluates the relationship between serum CK elevation and survival in patients with ALS and points to a lack of correlation. Thirty patients with ALS, who ranged in age from 21 to 73 years, were followed up from 7 to 57 months. All patients had neurologic and psychiatric evaluations, electromyographic examinations, and serum CK measurements. The CK level was elevated in 50% of the patients. On follow-up, 20 patients had died; ten of these had had elevated CK levels. The 3-year survival from the date of the examination was 47% for patients with elevated CK levels and 40% for patients with normal levels. This difference did not have statistical significance (p greater than 0.43).