This protocol requires 2-4 h and presents a method for injecting tumor cells, cancer stem cells or dispersed biopsy material into subcutaneous or orthotopic locations within recipient mice. The tumor cells or biopsy are mixed with basement membrane matrix proteins (CultrexBME or Matrigel) at 4 °C and then injected into recipient animals at preferred anatomical sites. Tumor cells can also be co-injected with additional cell types, such as fibroblasts, stromal cells, endothelial cells and so on. Details are given on appropriate cell numbers, handling and concentration of the basement membrane proteins, recipient animals, injection location and techniques. This procedure enables the growth of tumors from cells or biopsy material (tumor graft) with greater efficiency of take and growth, and with retention of the primary tumor phenotype based on histology. Co-injection with additional cell types provides more physiological models of human cancers for use in drug screening and studying cancer biology.