This report examines the effect of recombinant murine interleukin‐10 (rmIL‐10) on antigen‐induced β‐hexosaminidase, leukotriene (LT)C₄ and cytokine release from mouse bone marrow‐derived mast cells (BMMC). BMMC sensitized to hapten‐monoclonal IgE directed against dinitrophenol‐bovine serum albumin (DNP‐BSA) and challenged with 10 ng/ml DNP‐BSA generated β‐hexosaminidase and LTC₄‐like material, which was followed by tumor necrosis factor‐α (TNF‐α) and granulocyte‐macrophage colony‐stimulating factor (GM‐CSF) mRNA expression and protein release. Incubation of BMMC with 1–100 ng/ml rmIL‐10 inhibited cytokine generation, without affecting β‐hexosaminidase and LTC₄‐like material release. TNF‐α, but not GM‐CSF mRNA expression, was also diminished in rmIL‐10‐treated BMMC, suggesting that down‐regulation of cytokine production by rmIL‐10 involves different mechanisms. These results identify a novel biological action of IL‐10 as an inhibitor of cytokine production by stimulated mast cells.