Abstract: A diagnostic method is described for determining the treatment modality for neoplastic (cancer) tissue within the peritoneal cavity of a patient. The method utilizes a laparoscope with a visual display output as well as a radiation responsive instrument. These instruments are employed first to carry out a visual survey of the colon and then a radionuclide survey of the colon to locate concentrations of radiolabeled locator. A next survey is carried out with the radiation responsive instrument to determine the location of lymph node involvement in the cancer as well as other metastatic disease. Should the latter involvement be found, open laparotomy is indicated as the treatment modality. On the other hand, where no lymph node involvement is determined and the region of locator concentration can additionally be visualized, then conventional laparoscopic resection procedure is the determined treatment modality.