All cell functions, including cell proliferation, cell death and differentiation, as well as maintenance of health status and development of disease, are controlled by a multitude of genes and signaling pathways. New techniques such as cDNA microarrays have enabled us to analyze global gene expression 1-3 . However, almost all cell functions are executed by proteins, which cannot be studied simply through DNA and RNA techniques. Experimental analysis clearly shows a disparity between the relative expression levels of mRNA and their corresponding proteins 4 . Therefore, analysis of the protein profile is critical. Currently, two-dimensional polyacrylamide SDS page coupled with mass spectrometry is the mainstream approach to analyzing multiple protein expression levels 5,6 . However, the requirement of sophisticated devices and the lack of quantitative measurements greatly limit their broad application. Thus, effective study of multiple protein expression levels has been complicated, costly are time-consuming until now. Our Human Cytokine Antibody Arrays are the first commercially available protein array system 7-11 . By using the system, scientists can rapidly and accurately identify the expression profiles of multiple cytokines in several hours inexpensively. The kit provides a simple array format, and highly sensitive approach to simultaneously detect multiple cytokine expression levels from conditioned media, patient's sera, cell lysate, tissue lysates and other sources. Traditionally, cytokines are detected by using ELISA. However, This approach has several advantages over ELISA. First, and most importantly, our approach can detect many cytokines simultaneously. Secondly, sensitivity is greatly increased. As little as 4 pg/ml of MCP-1 can be detected using the protein array format. In contrast, at least 40 pg/ml of MCP-1 is required to produce a clear signal in an ELISA assay. Furthermore, the detection range is much greater than ELISA. For example, the detection range of IL-2 varies from 25 to 250,000 pg/ml using technology, whereas the detection range varies only within 100-1000 fold in a typical ELISA. Therefore, the detection range is greater with protein array compared with ELISA. The variation is lower than ELISA as well. As determined by densitometry, the variation between two spots ranged from 0 to 10% in duplicated experiments. In contrast, variation (about 20%) in ELISA is much higher. Finally, the system is much quicker and can be much easier to adapt to high-throughput technique. Pathway-specific array systems allow investigators to focus on the specific problem and are becoming an increasingly powerful tool in cDNA microarray systems. The first protein array system, known as Human Angiogenesis antibody array, is particularly useful in comparison with the human cytokine cDNA microarray system. Besides the ability to detect protein expression, the system is a more accurate reflection of active cytokine levels because it only detects secreted cytokines, and no amplification step is needed. Furthermore, it is much simpler, faster, environmentally friendlier, and more sensitive. Simultaneous detection of multiple cytokines undoubtedly provides a powerful tool to study cytokines. Cytokines play an important role in innate immunity, apoptosis, angiogenesis, cell growth and differentiation 12 . Cytokines are involved in most disease processes, including cancer and cardiac diseases. The interaction between cytokines and the cellular immune system is a dynamic process. The interactions of positive and negative stimuli, and positive as well as negative regulatory loops are complex and often involve multiple cytokines. Without doubt, simultaneous detection of multiple cytokines provides a powerful tool to study cytokines.