Cells of the B-cell lineage play an essential part in the immune response, not only as the producers of antigen-specific antibodies, but also as antigen-presenting cells. Unlike T cells, however, the establishment of long-term normal B-cell lines has proved to be exceedingly difficult. In this paper we demonstrate that cell membrane-expressed CD154 (CD40 ligand) is able to support the continual growth of porcine mesenteric lymph node B-cell cultures for more than 4 months without the addition of exogenous cytokines, such as interleukin-4 (IL-4). Addition of IL-4, but not interferon-gamma (IFN-gamma) or IL-13, to these cultures enhanced proliferation, as, to a lesser extent, did addition of IL-2. Interestingly, however, whilst IFN-gamma-supplemented cultures largely consisted of immunoglobulin M (IgM)-positive cells, cultures with IL-13 or IL-4 contained a significantly increased proportion of IgG-positive cells.