Human monocytes that have been isolated and purified from the peripheral blood have been demonstrated to be capable of killing tumor targets in vitro following activation to cytotoxicity by interferon-gamma. The purpose of this study is to determine if autologous activated monocytes can be used as an effective form of adoptive immunotherapy for colon cancer patients with disease spread to the peritoneal cavity. This protocol is based on a previous BRMP protocol which employed a similar study design; however, the patient population had undergone laparotomy and complete surgical excision of all macroscopic tumor. The patients in that protocol tolerated leukapheresis and infusions of activated monocytes along with interferon-gamma with tolerable toxicity. This study will enroll patients who have measurable macroscopic disease to determine whether adoptively transferred activated monocytes have cytocidal activity against established tumor. Because the disease is limited to the peritoneal cavity, the infused monocytes will have adequate contact with the tumor deposits, and questions of trafficking should not complicate the analysis of their efficacy. Although the protocol has been open to patient entry for the past year, no patients were enrolled on the protocol due to the existence of a competing protocol using intraperitoneally administered interleukin-2 plus LAK cells. Now that protocol has been closed, it is expected that patient accrual will be significant for this study over the next two years.