An adequate blood level of cyclosporine-A (CsA) is essential to keep graft function in kidney transplants. Due to a narrow therapeutic index and highly variable pharmacokinetic properties associated with CsA, drug interactions may have a significant impact on the immunosuppressive efficacy or toxicity of CsA. Numerous drug interactions of potential clinical significance involving CsA have been reported. Dephenyl-dimethyl-dicarboxylate (PMC), a hepatotonic drug, is a substance derived from the synthesis of Schizandrae fructus elements. We have experienced two cases of drug interaction between CsA and PMC in kidney transplants with chronic hepatitis. In both cases, CsA troughs decreased markedly to a subtherapeutic level following administration of PMC. We, therefore, suggest that PMC could decrease the CsA trough level and thus a close monitoring of the CsA trough level is necessary during a PMC therapy.