In the present study we have determined the content of hematopoietic and stromal progenitors in multiple myeloma (MM) bone marrow, and assessed their in vitro growth. Marrow cells were obtained from 17 MM patients at the time of diagnosis, and from 6 hematologically normal subjects. When mononuclear cells (MNC) from MM marrow were cultured, reduced numbers of hematopoietic progenitors were detected and their growth in long-term cultures was deficient, as compared to cultures of normal cells. When cell fractions enriched for CD34(+) Lin(-) cells were obtained, the levels of hematopoietic progenitors from MM marrow were within the normal range, and so was their growth kinetics in liquid suspension cultures. The levels of fibroblast progenitors in MM were not statistically different from those in normal marrow; however, their proliferation potential was significantly reduced. Conditioned media from MM-derived MNC and stroma cells contained factors that inhibited normal progenitor cell growth. Our observations suggest that hematopoietic progenitors in MM marrow are intrinsically normal; however, their growth in LTMC may be hampered by the presence of abnormal accessory and stroma cells. These results suggest that besides its role in the generation of osteolytic lesions and the expansion of the myeloma clone, the marrow microenvironment in MM may have a negative effect on hematopoiesis. Copyright © 2010 Elsevier Ltd. All rights reserved.