A physiological three-dimensional culture system was developed for the growth of human bone marrow. Bone marrow stromal cells were established on a nylon filtration screen template, suspended in liquid medium and grown to 70% confluence, and inoculated with hematopoietic cells. An intricate microenvironment is established to support hematopoiesis, which proceeds in a three-dimensional orientation. Analysis of the adherent zone of these cultures with flow cytometry and progenitor cell assays reveals multilineage hematologic expression and active proliferation of immature cells for the 12 week experimental period. Similar results were obtained with rat bone marrow cultures using this methodology. The suspended nylon mesh system is novel in that it supports the growth of several hematologic lineages concurrently. This system may lend itself to the growth of purged or untreated bone marrow for transplantation.