We report a 54 years old male that received a renal allograft without complications. One year after the transplantation, she was receiving cyclosporine doses of 2 to 3 mg/kg and maintained serum levels of 60 to 90 mg/dl. An abrupt increase in cyclosporine serum levels to 469 and 600 mg/dl was noted after 15 months of transplantation. After a careful interrogation the patient admitted the use of Geum chiloense ("hierba del clavo"). Discontinuing this herbal remedy, cyclosporine levels decreased to 55 mg/dl, despite the maintenance of tbe same cyclosporine dose. The potential side effects of herbal remedies must be borne in mind (Rev Med Chile 2001; 129: 789-90).