To the Editor: Because of the uniformly bad prognosis for patients with amyotrophic lateral sclerosis (ALS) it is important that any possible treatment for the disease be evaluated as thoroughly and promptly as possible. Recently, it was suggested that a synthetic agent, isoprinosine, produced clinical improvement in at least one patient with ALS. This drug is thought to effect a change in the conformation of polyribosomes, and this biochemical action may be the basis for its antiviral activity demonstrated in vitro. Although the rationale for its possible effect in patients with ALS is not certain, it is not toxic to …. © 1971, Massachusetts Medical Society. All rights reserved.