A number of publications contain contradictory data about influence of mesenchymal stromal cells (MSC) on B-lymphocyte growth, differentiation and production of immunoglobulins (Ig). The aim of the study was to investigate the influence of MSC derived from adipose tissue of healthy donors and cancer patients on the proliferation and Ig synthesis of lymphoblastoid cell line Namalva and myeloma cell line U266. Co-cultivation of Namalva cells with MSC stimulated their proliferation, decreased the doubling time and the minimal effective seeding dose and therefore made cloning of these lymphoblastoid cells possible. The presence of MSC supported the survival and proliferation of Namalva cells cultivated in growth factor deficient medium. MSC also stimulated proliferation of U266 myeloma cells. Both MSC derived from adipose tissue from the healthy donors and from patients with breast cancer effectively stimulated B-cell lines proliferation. Presence of MSC in mixed cultures had no influence on the production of IgM or IgE by Namalva or U266 cells respectively. Co-cultivation of Namalva or U266 with MSC resulted in the formation of close intercellular contacts between cells of both types.