We have investigated the phenotypic and functional characteristics of murine pre‐B cells obtained in semisolid and liquid culture with stem cell factor (SCF) and interleukin 7 (IL‐7). Both serum‐supplemented and serum‐deprived culture conditions were used. The source of bone marrow cells was either normal mice (CD1 and C3H) or the lupus strain of mice MRL/Ipr and its congenic strain MRL/+. SCF (100 ng/ml) and IL‐7 (250 ng/ml) supported murine B cell proliferation in vitro from all the murine strains analyzed both in serum‐supplemented and serum‐deprived conditions. Maximal colony growth was observed in both cases when the factors were used in combination. The growth factors alone induced some colony growth in serum‐supplemented cultures but were either ineffective or had modest activity in serum‐deprived cultures. Cells harvested from the colonies or generated in liquid cultures and stimulated with SCF + IL‐7 in the absence of serum had almost exclusively a pre‐B cell phenotype (BP‐1+, B220+, slg‐, CD4‐, CD8‐, Mac‐1, RB‐6‐). Both the maximal colony growth in semisolid culture and the maximal number of cells in liquid culture were observed at day 12–14. At this time, the pre‐B cells failed to differentiate further and started to die. Pre‐B cells generated in vitro were, however, capable of differentiating in vivo. SCID mice injected with 2 × 106 pre‐B cells had readily detectable serum levels of IgM (54 ± 26 m̈g/ml) and IgG (60 ± 95 m̈g/ml) at 4 weeks and 6 weeks posttransplantation, respectively. Mature B and T cells of the donor major histocompatibility complex type were detected in the SCID mice at sacrifice 14 weeks posttransplantation. These data indicate that purified (>80% BP‐1+) populations of functional pre‐B cells can be grown from murine bone marrow of normal mice as well as of lupus mice in serum‐deprived cultures stimulated with SCF and IL‐7. These cultures, therefore, provide a highly enriched source of pre‐B cells but also contain T cell precursors that differentiate upon adoptive transfer into SCID mice. © 1995 Wiley‐Liss, Inc.