We examined the expression level of androgen receptor (AR) messenger RNA (mRNA) in the motoneurons from patients with X-linked spinal and bulbar muscular atrophy (SBMA) and amyotrophic lateral sclerosis (ALS) using in situ hybridization. Although AR mRNA was detected in motoneurons from the SBMA patient, the expression level was lower than that from the patients with ALS, despite similar loss of motoneurons. The expression level of AR mRNA in the dorsal nucleus of Clarke from the patient with SBMA was similar to that in the patients with ALS, suggesting that the qualities of the mRNA were similar in each spinal cord sample and that AR mRNA was uniquely reduced in the motoneurons of the SBMA patient. Decreased levels of AR mRNA may be involved in the pathogenesis of SBMA resulting in degeneration of motoneurons.