This study was motivated by the need to develop new methods to predict tumor response to chemotherapeutic agents. Using implantable cell-growth chambers, squamous carcinoma cells from head and neck tumors were xenografted into the peritoneal cavity of immunocompetent rats. Animals were divided into control and treatment groups. The treatment groups received intravenous cisplatin (CDDP) or 5-fluorouracil (5-FU) v normal saline solution for the control. Animals from each group were randomly selected and killed on days 3, 5, and 7 postimplantation. The chambers were retrieved, the media aspirated, and cells counted. Exponential growth curves were derived for the control and treatment groups. Statistically significant growth inhibition was observed for both treatment arms, compared with controls. This method of chemosensitivity testing proved to be inexpensive and reliable, and demonstrated tumor cell killing by 5-FU and CDDP.