The interferon-α and -β (IFN-α/β) producing ability of the two murine dendritic cell (DC) lines D2SC/1 and FSDC was studied. The D2SC/1 cells produced IFN-α and -β when stimulated by herpes simplex virus (HSV), Sendai virus (SV) or by the bacteria Escherichia coli or Staphylococcus aureus Cowan I. Precultivating (priming) D2SC/1 cells with recombinant IFN-β or a combination of IFN-β and granulocyte–macrophage colony-stimulating factor increased production of IFN-α/β induced by HSV or the bacteria, but not by SV. Also, the kinetics of IFN-α/β responses were different for SV compared to HSV and the bacteria, suggesting different induction mechanisms. The FSDC cells differed from the D2SC/1 cells mainly in that predominantly IFN-β was produced, that little or no IFN-α/β production was induced by the bacteria, and that the IFN-α/β responses were most efficiently primed by IFN-γ. Priming the DC lines with tumour necrosis factor-α, interleukin-10 (IL-10) or IL-4 did not affect the IFN-α/β response induced by HSV. The results show that the two DC lines provide a convenient tool to study the induction and control of the IFN-α/β response, as well as the immunoregulatory role of IFN-α/β produced by DC.