Emodin and scoparone, the active principles isolated from Polygonum multiflorum and Artemisia scoparia, respectively, both exhibit vasorelaxant and immunosuppressive effects. Emodin (10(-6)-3 x 10(-5) M) and scoparone (10(-6)-3 x 10(-5) M) dose dependently relaxed rat thoracic aortic rings precontracted with phenylephrine. Emodin (3 x 10(-7)-10(-4) M) and scoparone (10(-6)-3 x 10(-4) M) also dose dependently suppressed the responses of human mononuclear cells to phytohemagglutinin and mixed lymphocyte reaction. These compounds may be useful as new templates for the development of better immunosuppressive agents with vasorelaxant actions for use against transplantation rejection and autoimmune disease.