In ten patients with amyotrophic lateral sclerosis (ALS) and 146 control subjects, the cellular inflammatory response was studied by the "skin window" technique and 24 hours after inflicting the lesion. In all patients with ALS the migration of macrophages into the inflammatory field was retarded, and in three patients the total number of cells was decreased. This alteration could be due to a latent disorder of the autonomic nervous system.