In response to antigen stimulation, T(h) cells differentiate into two types of effector cells, T(h)1 and T(h)2. T(h)1 cells predominantly mediate cellular immunity, whereas T(h)2 cells induce humoral allergic responses. We have conducted here serial analysis of gene expression (SAGE) in human activated T(h)1- and T(h)2-polarized cells from cord blood. SAGE analysis of 64,510 tags (32,219 and 32,291 tags from T(h)1 and T(h)2 cells respectively) allowed identification of 22,096 different transcripts. In activated T(h)1 cells, many of the known genes (12 genes, P: < 0.01; 56 genes, P: < 0.05), including genes encoding IFN-gamma, lymphotactin, osteopontin, MIP-1alpha, MIP-1beta, perforin, beta-catenin and CD55, are highly expressed. On the other hand, in activated T(h)2 cells rather limited numbers of known genes (four genes, P: < 0.01; 10 genes; P: < 0.05), such as genes encoding FUS, ILF-2, IL-13 and E2-EPF, are found to be selectively expressed. The comprehensive identification of genes selectively expressed in human activated T(h)1 or T(h)2 cells should contribute to our understanding of the molecular basis of T(h)1/T(h)2-dominated human diseases and may provide genetic information to diagnose these diseases.