The 3-dimensional reconstructed bone marrow model system permits expansion of numerous cell types, including clonal myeloma cells. Nonproliferating myeloma cells concentrate at the reconstructed endosteal-marrow junction and may represent drug-resistant myeloma cancer stem cells. This biologically relevant model system provides a means to test the sensitivities of all cellular components of the myeloma clone, as well as test for undesirable toxic side effects on other cell types naturally present in the bone marrow microenvironment. Illustration by Debra T. Dartez.