The administration of phthalazinol, in a daily dose of 1.2g or 20mg/kg, has been shown to retard or to stop the progression of their muscle atrophy, at least for 3 to 6 months of the present observation period, in all 9 patients suffering from hitherto desperate condition of amyotrophic lateral sclerosis without recognizable side effect. Two patients exhibited a marked increase in the strength of their moderately affected muscles.