In an attempt to characterize genes participating in the allergic late phase reaction, we have isolated a novel intercrine/chemokine (called MARC) from a cDNA library of the stimulated mouse mast cell line, CPII. As measured by Northern blotting, it is strongly upregulated at the mRNA level after the physiological challenge of the cells with immunoglobulin (Ig)E plus antigen. Unstimulated cells completely lack significant, stable expression, as do a number of other, different cell lines (uninduced and induced) and mouse tissues. In contrast to the Northern blot analysis, a polymerase chain reaction (PCR) analysis, performed on CPII cells and on Percoll gradient purified mouse peritoneal mast cells, revealed a basal level of transcription in the uninduced stage. After 2 h of IgE plus antigen challenge, a quantitative reverse transcriptase-PCR, using a spiked in MIMIC, showed a level of transcripts more than 100-fold higher in the CPII cells and 5-20-fold higher in purified mouse peritoneal cavity mast cells. This rapid induction after the Fc epsilon RI challenge, the identification of the gene as a member of the chemokine family, and its upregulated expression in peritoneal mast cells, all suggest an involvement in certain acute and chronic pathological mast cell-driven diseases.