The Clinical Applications Core Technology, (CACT), laboratory provides both clinical and research investigators at St Jude Children's Research Hospital with state of the art Affymetrix GeneChip® technology. Affymetrix GeneChips® are manufactured with a technology borrowed from the semiconductor industry called photolithography. Combined with combinatorial chemistry, the technology is capable of printing over 6 million features on an array. Affymetrix array technology lends itself to an extensive range of genome analysis from gene expression profiling and SNP (Single Nucleotide Polymorphism) analysis to novel RNA transcript discovery. Since the opening of the facility in the summer of the year 2000, we have run over 9,000 gene expression Affymetrix chips and over 6,000 Affymetrix human mapping arrays for SNP analysis. To date, we have supported the research efforts of 50 laboratories within the institution. Research projects have included those examining gene expression in leukemias, lymphomas and a variety of other solid tumors. Establishing these cancer-associated expression profiles enhances diagnostic capabilities, guides the tailoring of cancer treatment protocols towards maximal effectiveness and minimal residual damage, and provides important clues regarding the molecular nature of different cancers. The molecular effect of specific drugs on leukemic cells is also being examined. These experiments also provide important information valuable in the design of cancer cell-specific treatment protocols, as well as basic information about the bioavailability and biochemical effects of the drug itself. Developmental and differentiation pathways in a wide variety of cells important for immune responses are being examined. Likewise, developmental, metabolic and differentiation pathways for prokaryotic organisms like E. coli, as well as neural, hematopoietic, myeloid, and lymphoid cells, are being mapped.