PURPOSE: Percutaneous microwave coagulation therapy (PMCT) uses a new energy source, microwave, in the treatment of solid neoplasms. We evaluated the efficacy of PMCT for nodular hepatic tumors in nine patients. MATERIALS AND METHODS: Between December 1998 and June 1999, we performed PMCT in six patients with hepatocellular carcinoma (HCC), two with one and three metastatic nodules each from colon cancer, and one with adenomatous hyperplasia. Four patients were female and five were male, and their age ranged between 44 and 71 (mean, 58.8) years. Under sonographic guidance a 14-gauge guiding needle was inserted percutaneously toward the lesion, and within it a needle electrode was precisely positioned. Microwave 2450MHz in frequency and with 60 or 80 watt emission was generated for 80~90 seconds. We evaluated the ultrasound findings obtained during the procedure, pre-PMCT and follow-up CT images, changes in tumor marker(AFP or CA19-9) levels and the results of liver function tests, and complications arising during the six-month period following PMCT. RESULTS: Immediately after microwave emission, characteristic hyperechogenicity appeared on the realtime sonogram. Two patients with HCC underwent CT before PMCT, and typical enhancement during the arterial phase and washout during the portovenous phase was observed. In one patient, two metastatic lesions from colon cancer showed delayed enhancement on pre-PMCT CT. Initial follow-up CT, performed between 1 and 4 weeks after the PMCT procedure, showed that eight lesions-including two HCCs which were highly enhanced on CT before PMCT-showed no contrast enhancement, and three others showed delayed enhancement. Two of the eight lesions which showed no contrast enhancement at initial follow-up CT were markedly decreased in size (from 2.9 and 4.0 cm to 1.0 and 2.0 cm, respectively) at subseqent follow-up 3 months and 6 months later, respectively. One of the three lesions showing delayed enhancement had increased in size from 4.1 to 5.5 cm at subsequent follow-up CT, 2 months later. Serum AFP or CA19-9 levels decreased in four of six patients (66.7%) who were followed up for 6 months. Transient elevation of aspartate aminotransferase(AST) levels were noted in all patients. PMCT-related complications included intrahepatic arterioportal shunt in two patients, pleural effusion in one, skin burn in one, intraperitoneal hemorrhage in one, and mild fever, abdominal pain and nausea in seven. No complications were serious, however. CONCLUSION: Our preliminary experiences suggest that PMCT is a safe and effective treatment modality for nodular hepatic tumors.