Activated lymphocytes induced by mitogens or antigens express various sets of genes, including those involved in the expression of cytokines, surface molecules, and nuclear proteins. To detect inducible genes in activated lymphocytes, we used the RNA arbitrarily primed polymerase chain reaction (RAP-PCR) method, which is modified by original differential display. By this method we identified eight clones; four contained sequences almost identical to that of the genes for heat shock 90Kd protein1 alpha, STAT2, Ig kappa constant region and interferon receptor 1, two had 70% homology to mitochondrial ATP synthase and bromodomain-containing 2 genes, and two had less than 40% homology to known DNA sequences. By RT-PCR, the heat shock 90 Kd protein1 alpha, STAT2 and interferon receptor 1 genes showed increased expression in phytohemagglutinin (PHA)-stimulated or antigen stimulated T cell line. Differential display is a useful method for detection of inducible genes from a small amount of material and at various time points, although the homology of PCR primer influences the displayed genes.