Apart from an increased risk of graft rejection, the interaction also had cost implications because the dosage of this expensive drug had to be increased. In the period from 1995 to April 2000 an amount of approximately 15,300.- [symbol: see text] (30,000.- DM) of cyclosporine medication was necessary to avoid transplant rejection. The trend of the graphs strongly suggests that the treatment with St John's wort was the cause of the drop in plasma cyclosporine. It is of particular interest since this long-term observation uniquely reveals the raise of costs.