CD34+ CD117+ cells in human peripheral blood have mast cell-forming capacity. We have identified highly committed mast cell progenitors as Lin- CD34+ CD117 intermediate/high FcεRI+ cells. To explore the gene expression profile of the highly committed mast cell progenitors, we performed whole-transcriptome microarray analyses of the cells and compared them with mature basophils. Overall design: Mast cell progenitors and mature basophils from human blood were isolated from 3 subjects using fluorescence-activated cell sorting and whole-transcriptome microarray analyses were performed.