Sebum production is under hormonal control. We had shown that male sex is associated with more severe disease in Behçet's syndrome and the acneiform skin lesion of this disorder is not different from ordinary acne, an androgen-dependent lesion. Sebum excretion rate was higher in patients with Behçet's syndrome than in healthy controls, children and patients with ankylosing spondylitis. On the other hand, patients with rheumatoid arthritis had high levels of sebum excretion rate comparable to those found in patients with acne vulgaris. These suggest the presence of a sebotrophic hormone and/or other hormonal effects in Behçet's syndrome and rheumatoid arthritis.