Novel cyclized .omega.-carboxyethyl mono- or dithiocarbanilic acids are disclosed as immunoregulatory agents, useful in the treatment of organ transplant reject phenomenon and autoimmune diseases particularly where a delayed hypersensitivity component has been established, such as multiple sclerosis. Additionally described is the use of certain cyclized .omega.-carboxyalkyl mono- or dithiocarbamic acids and certain cyclized .omega.-carboxyalkyl mono- or dithiocarbamic acids.