• Patients with Reye's syndrome (RS) whose degree of severity was classified as stage 0 (alert and awake) were compared with patients with a severity classification of stage 1 or greater. The centers for Disease Control case definition and staging criteria were used. Two hundred twenty-seven patients with RS were investigated by the Ohio Department of Health from Dec 1, 1978, through March 31, 1980. There were 67 identified patients who never exceeded stage 0 and 160 patients classified as stage 1 or greater. Both groups of patients were compared according to demographic features, symptomatology, medication use during the antecedent illness, and laboratory findings during the RS illness. Stage 0 patients were similar to patients at stage 1 or greater in their demographic features, illnesses, medications preceding RS, and results of liver function tests; however, values of serum ammonia, creatine phosphokinase, prothrombin time, and bilirubin increased with RS severity.