SUMMARYCyclosporin A (CyA) is the forerunner of a new generation of immunosuppressive drugs. It is highly effective in both antibody‐ and cell‐mediated immunity and in inhibiting chronic inflammatory reactions. Cyclosporin A is, therefore, widely used to prevent rejection in clinical organ transplantation and appears to be very promising in the treatment of several autoimmune diseases, in particular psoriasis. Cyclosporin A is not only effective when given at the time of sensitization (prevention of rejection), but also when administered therapeutically during an immune response, such as during the active course of an autoimmune disease. The most important aspect of its immunosuppressive mechanism is the inhibition of lymphokine production secreted by activated T cells. The pharmacological effects of CyA are rapid in onset, dose‐dependent and often quickly reversible when treatment is st