In order to elucidate the relationship between certain neuromuscular diseases and gonadal hormones, we measured the levels of serum estrogens and other sex-related hormones. The values were compared with those for age-matched controls. The cases, comprising bulbospinal muscular disease of the Kennedy-Alter-Sung type, Kugelberg-Welander disease, amyotrophic lateral sclerosis, and Duchenne muscular dystrophy, were all euthyroid males. The baseline levels of serum estrone were significantly higher in all of the patients than in age-matched normal subjects. Serum baseline testosterone, LH and FSH levels were all essentially normal, except low FSH levels in Duchenne muscular dystrophy. Since our patients had no overweight, liver or glandular abnormalities, we presume that the elevated serum estrone levels have resulted from increased peripheral androgen-to-estrogen conversion.