Thirty-two patients affected by amyotrophic lateral sclerosis (ALS) were included in a controlled, open therapeutic trial with branched chain amino acids (BCAA). Patients with bulbar muscle involvement were evaluated separately. No statistically significant differences were found in the clinical outcome between the patients treated and the control groups. Blood L-glutamate levels measured in eight patients were normal. The failure of BCAA in the treatment of the patients could be due to different disorders with unpredictable outcome included under the diagnosis of ALS.