Epidermal growth factor (EGF), a mitogenic peptide, is widely distributed within the brain and endocrine cells of the gastro-intestinal tract. Using EGF radioreceptor assay, the EGF level was measured in lumbar cerebrospinal fluid from five patients with amyotrophic lateral sclerosis (ALS) and seven patients with intervertebral disc disease as a control group. The patients with ALS showed reduced EGF levels to 662.4 +/- 207 pg/ml as compared with controls 1013 +/- 182.8 pg/ml (P less than 0.02). These results indicate a possible EGF involvement in the pathogenesis of ALS.