Dendritic cell (DC) maturation is the process by which immature DC in the periphery differentiate into fully competent antigen-presenting cells that initiate the T cell response. However, DC respond to many distinct maturation stimuli, and different types of mature DC induce qualitatively different T cell responses. As DC maturation involves the coordinated regulation of hundreds of genes, comprehensive assessment of DC maturation status would ideally involve monitoring the expression of all of these transcripts. However, whole-genome microarrays are not well-suited for routine phenotyping of DC, as the vast majority of genes represented on such chips are not relevant to DC biology, and their cost limits their use for most laboratories. We therefore developed a DC-dedicated microarray, or "DC Chip", incorporating probes for 121 genes up-regulated during DC maturation, 93 genes down-regulated during maturation, 14 DC-specific genes, and 90 other genes with known or probable immune functions. These microarrays were used to study the kinetics of DC maturation and the differences in maturation profiles among five healthy donors after stimulation with tumor necrosis factor-alpha + polyI:C. Results obtained with the DC Chip were consistent with flow cytometry, enzyme-linked immunosorbent assay, and real-time polymerase chain reaction, as well as previously published data. Furthermore, the coordinated regulation of a cluster of genes (indoleamine dioxygenase, kynureninase, kynurenine monoxygenase, tryptophanyl tRNA synthetase, and 3-hydroxyanthranilate 3,4-dioxygenase) involved in tryptophan metabolism was observed. These data demonstrate the use of the DC Chip for monitoring the molecular processes involved in the orientation of the immune response by DC.