Background : Economic evaluation of clinical pharmacokinetic consultation services for theophylline, which is being widely used recently, is considered in patients for both proper care and cost efficiency. Mathods : This is a cost-benefit analysis of clinical pharmacokinetic consultation service for theophylline. Trial groups were chosen from 2 general hospitals which was performing clinical pharmacokinetic consultation- services in 1998. Control group was chosen from another one general hospital. The analysis includes 25 patients (sample patients) for trial group and 17 patients for control group. Results : On the basis of incremental analysis, it is estimated that the total (direct and indirect) annual costs of the clinical, pharmacokinetic services of theophylline for the patients in the trial group was about 65 million, whereas total annual benefits from those services was estimated to be about 551 million. The net benefits incurred to the sample patients, thus calculated, was about 485 million per year. In the analysis, we assumed that indirect benefits accruing to those services were non-existent. If that amount was included, the estimated net benefits would be much greater than the calculated one. Conclusion : We found that clinical pharmacokinetic consultation services for theophylline could produce more marginal benefits than marginal costs by those services from the social point of view. More controlled prospective trial in the future would be helpful for affirmation of the results of this study.