A double-blind, placebo-controlled trial of single doses of thyrotropin releasing hormone (TRH) was performed on 12 patients with amyotrophic lateral sclerosis. Each patient was given subcutaneous injections of TRH 150 mg or placebo, and IV infusions of TRH 500 mg or placebo at 72- to 96-hour intervals. Eight motor and functional ratings were scored at regular intervals after each injection. Side effects were seen in all patients and were obvious to patients and examiners, making true blinding impossible. Nevertheless, statistically significant improvement was seen only in dynametric strength 1 hour after subcutaneous injection (p less than 0.05). Significant improvement occurred, in one patient only, on subjective speech testing during IV infusion of TRH. In none of six other ratings was there a significant difference between TRH and placebo. Subjective improvement was noted by 11 of 12 patients.