Monocytes/macrophages play a key role in host defense by phagocytosing invaded pathogens, presenting antigens to immune cells and producing numerous inflammatory mediators. Although the expression of many proteins and genes has been described to be up-regulated in activated human monocytes, a complete picture of the pathophysiological function of activated human monocytes has not yet been drawn. In this study the serial analysis of gene expression (SAGE) procedure was applied to lipopolysaccharide (LPS)-stimulated human monocytes. A total of 35,874 tags corresponding to more than 12,000 different transcripts was sequenced. In addition, the Long SAGE procedure was conducted in LPS-stimulated monocytes to increase the accuracy of corresponding gene identification. Comparison of the gene expression profile with that of resting monocytes revealed the whole LPS-inducible gene expression profile. The functional classifications of LPS-inducible genes (> or = 8-fold increase compared with resting monocytes) in monocytes showed that 25% of inducible genes were identified to encode cytokines and chemokines, followed by proteins related to metabolism (11%), cell surface antigens (9%), nuclear proteins (8%), proteases (6%), proteins related to extracellular transport (4%) and intracellular transducers (4%). Moreover, 14% of LPS-inducible genes still encode proteins with unknown function. This study represents the first global analysis of LPS-inducible genes in human monocytes and provides tremendous novel information for the function of LPS-activated monocytes and targets for diagnosing, monitoring and treating sepsis and various human infectious and inflammatory diseases.