The question remains as to whether metastatic cells (cancer seed) that eventually colonize a particular organ (cancer soil) have specific properties that distinguish them from the other cells of the primary tumor. However until recently there have not been model systems in which this question could be fully answered. To further understand the relationship between seed and soil we have developed an orthotopic-transplantation nude-mouse model that allows human tumors to essentially replicate their behavior they had in the patient. The patient-like behavior of the transplanted human tumor in the nude mouse depends on the use of intact tumor tissue for orthotopic transplantation. Here we report that a colorectal tumor lung metastasis surgically resected from a patient could grow in nude mouse lung, but not in either the colon or the subcutis after transplantation of intact tissue. The results were striking in that the human colorectal tumor lung metastasis grew in the lung of the animals and not in the colon or in the subcutis of the animals. The results described here suggest that the lung metastasis of the patient colon tumor is distinct in its soil requirement from the majority of the cells of the original colon tumor. In contract, in the intact-tissue orthotopic transplant model, primary human colon tumors grow when transplanted to the colon of the nude mouse. Thus the colorectal cancer "seed" which metastasized to the lung in the patients seems very selective for the "soil" of the lung of both the patient and the nude mouse.