Mast cells play important roles in allergic and inflammatory diseases. Efforts to better understand human mast cell activation and develop novel inhibitory agents have been hampered by the lack of suitable human mast cell lines. The HMC-1 mast cell line has been extensively used, but lacks native expression of the human high-affinity IgE receptor FcεRI limiting its applications. We have stably transfected HMC-1 cells with the IgE-binding α-subunit of FcεRI to generate HMCα cells that are antigen-responsive. We have used flow cytometry, cell signaling assays, pharmacological pathway inhibitors and cell functional assays to characterize the properties of HMCα cells. IgE/antigen responses were compared with those of the adenosine receptor agonist NECA. Surface expression of FcεRI in HMCα cells was demonstrated and was enhanced by prior sensitization with IgE. Activation of HMCα cells with IgE/antigen did not produce degranulation, but did lead to release of numerous cytokines. Whilst there was no measurable increase of intracellular Ca(2+) or marked general changes in protein tyrosine phosphorylation, IgE/antigen stimulation of HMCα cells enhanced phosphorylation of p38(MAPK) and Erk. Inhibitors of these pathways, as well as the src kinase inhibitor PP2, attenuated IgE/antigen-induced cytokine release. In summary, we have generated and characterized HMCα cells and show that they are a useful and relevant human mast cell model to examine FcεRI stabilization, signaling and mediator release. We envisage that HMCα cells will have utility in understanding the importance of mast cells in human allergic disease and in assessing the activity of novel anti-allergic compounds.