BACKGROUND: Therapeutic drug monitoring (TDM) has been shown to be effective in minimizing the risk for toxicity and maximizing the efficacy of the drugs. The application of pharmacokinetics principles to indiviualization and optimization of dosage is necessary. We evolved interpretative report system of digoxin determination in a view of individual's pharmacokinetics. The alto of the present study is to validate the effectiveness of the interpretative report system in digoxin therapeutic monitoring service. METHODS: We reviewed 125 inpatients of two groups. 4 group, before interpretative reporting, had 86 inpatients from February 1996 to March 1996. B group included 39 inpatients from September 1996 to October 1996 after the practice of the sytem. Digoxin concentrations were measured in serum by TDxFlex (Abbott Laboratories, U.S.A.). Each patient's digoxin pharmacokinetics was determined by using the Abbott-base Pharmacokinetics system (Abbott Laboratories, U.S.A.) . The interpretation for the assayed digoxin level, the recommendation of maintenance dosage and the simulation graph with predicted serum levels were included in the report. The effectiveness of the reporting system was evaluated by comparing the appropriateness of digoxin level measurement between both groups. RESULTS: It revealed that appropriate measurements of digoxin level were 59.5 % of the tests in A group and 77.1% of those in B group (p=0.006). Evaluation of serum digoxin concentrations stratified by digoxin concentration showed also significant difference among the percentage of tests in each concentration range between both groups (p=0.011). CONCLUSIONS: Interpretative report system for the assayed results caused to increase in the appropriateness of digoxin measurement. The report system with some improvement which is achieved through the active approach to physician helps us use TDM effectively. The system can be applied to the other TDM drugs.