PURPOSE: Fentanyl is a synthetic opioid and transdermal therapeutic system (TTS), designed to release the drug into the skin at a constant rate, ranging from 25 to 100 microgram/hr, for up to 3 days. For the control of chronic cancer pain, Durogesic(R) patches (Janssen Co., USA) are now widely used. Recently, the Hana Company in Korea developed a new fentanyl patch, Fentas(R) using a different method. To compare the efficacy, and safety, of the fentanyl patch manufactured in Korea (Hana Pharm. Co. Ltd), with the Durogesic(R) patch, in controlling cancer pain, we performed randomized controlled, open labelled, phase III studies. MATERIALS AND METGODS: From January 2000 to April 2001, 85 patients were enrolled, 69 of whom (42 in D arm and 43 in F arm) completed the study, and were therefore assessable for per protocol (PP) analyses. RESULTS: There were no significant differences between the two groups in baseline characteristics, with the exception of age. The primary end point was to show the therapeutic equivalence of the two patches. In these clinical trials, the confidence interval of difference, between the test drug (Fentas(R)) and the control (Durogesic(R)), was 0.027~ +0.124 by intention to treat (ITT) analysis. Even if the upper confidence interval exceeds + 0.1, the test drug is not superior to the control drug, because the confidence interval includes 0. However, by PP analysis, the confidence interval lies exactly within +/- 0.1. Therefore, we could conclude the two patches are therapeutically equivalent. The second endpoint was the difference of visual analog scale (VAS) between the baseline and the average of three measurements after treatment. The difference in VAS was 50.44+/-10.28 for the F arm, and 44.69+/-11.00 for the D arm. By PP analysis the test drug was superior to the control (p=0.028). The rescue morphine amount was 81.21+/-124.76 for F arm and 66.19+/-115.9 for D arm, and there was no significant difference between the two groups (p=0.6063). The most common adverse effects of both fentanyl patches were nausea or vomiting (55.3%), somnolence (50.0%), constipation (39.5%), gastrointestinal discomfort (57.9%) and headaches (25.0%). In general there was no significant difference in side effects or laboratory data between the two groups. CONCLUSION: These findings suggest that Fentas(R) patches, administered every 3 days, are effective, safe, and well tolerated for the treatment of most patients with cancer pain and is as effective or better than Durogesic(R).