In a hematopoietic microenvironment in vivo, spatial organisation of hematopoiesis is possible due to the existence of a three-dimensional framework, the main part of which is formed by a branching population of stromal cells. Most of the previous in vitro studies, concerning long-term bone marrow cultures, were based on a previously prepared, flat adherent layer of stromal cells. There are only few reports concerning the three-dimensional growth pattern of the bone marrow stroma. In the present study we used a new three-dimensional model of the stromal cell culture. The framework for the cultured stromal cells was a structure of a nonliving trabecular bone (Unilab Surgibone). After a period of about four weeks the stromal cells created a spatial network which filled the intertrabecular spaces of the spongy bone.