Coculture of mouse bone marrow-derived mast cells (BMMC) with fibroblasts in the presence of stem cell factor (SCF) facilitates morphological and functional maturation toward a connective tissue mast cell (CTMC)-like phenotype. By means of cDNA subtraction, we identified several inducible genes during this mast cell maturation process. Of approximately 100 sequenced clones induced, nearly 50% were chromosome 14-associated serine proteases. Approximately 14% encoded NDRG1, a 43-kDa cytosolic protein that has been implicated in cell differentiation. NDRG1 was distributed in the cytosol of cultured mast cells and CTMC in rat skin. Overexpression of NDRG1 in RBL-2H3 cells resulted in enhanced degranulation in response to various stimuli. Thus, NDRG1 may be a mast cell maturation-associated inducible protein that allows the cells to be susceptible to extracellular stimuli leading to degranulation. Additionally, several unique maturation-associated inducible genes were identified, molecular and functional characterization of which will provide new insights into mast cell biology.