Protirelin (thyrotropin-releasing hormone) appears to be a neuromodulator in the extrahypothalamic nervous system and has been suggested as an adjunct in the treatment of amyotrophic lateral sclerosis (ALS). Clinical studies have been divided on the efficacy of protirelin (TRH) despite strong experimental findings that are consistent with a role for the peptide in ALS. Recent findings provide evidence of a gender-related specificity in the ability of protirelin to potentiate the monosynaptic reflex. While castration in male neonatal rats lowered the sensitivity to protirelin, testosterone treatment restored that sensitivity. An examination of the clinical studies reveals a failure either to identify patients' sex or to separate the results on the basis of sex. These findings provide convincing evidence for the potential efficacy of protirelin in ALS if the patient's sex and underlying hormonal status are taken into account.