Complete surgical resection of stage III non-small cell lung cancer (NSCLC) is at times impossible. Adjuvant radiation therapy is required to sterilize the residual tumor. This study is to investigate the safety, reproducibility, and effectiveness of intraoperative I-125 or Pd-103 Gelfoam plaque implant technique as an adjuvant treatment for resected stage III NSCLC with positive surgical margin. Between 1989 and 1993, 12 patients with stage III NSCLC received intraoperative lung implant with radioactive I-125 or Pd-103 pellets. All 12 patients underwent tumor resection, but either gross or microscopic positive margin was found during operation. Radioactive I-125 or Pd-103 seeds were embedded in the Gelfoam plaque. After surgical resection was completed, the radioactive Gelfoam plaque was secured onto the tumor bed either by clips or suture. Either preoperative or postoperative external beam radiation of 45-60 Gy was given to all of the 12 patients. Four patients received chemotherapy. No patient has developed any early or late complications attributable to implant procedure or radiation. The local control rate at last follow-up is 82%. The 2-year overall and cause-specific survival rates are 45% and 56%, respectively. The intraoperative Gelfoam I-125 or Pd-103 planar implant technique is a safe, reproducible, and effective technique of treatment for stage III NSCLC with a positive surgical margin. Encouraging local control and survival are achieved in patients treated with this technique. This technique will compliment standard adjuvant treatments to further improve local control in resected state III lung cancer.