The interleukin-23 (IL-23) pathway plays a critical role in the pathogenesis of multiple chronic inflammatory disorders, however, inter-individual variability in IL-23-induced signal transduction in circulating human lymphocytes has not been well-defined. In this study, we observed marked, reproducible inter-individual differences in IL-23 responsiveness (measured by STAT3 phosphorylation) in peripheral blood CD8+CD45RO+ memory T and CD3+CD56+ NKT cells. To define mechanisms that might be contributing to the differential IL-23-induced STAT3 activation between individuals, we examined mRNA expression differences in CD8+CD45RO+ memory T cells between IL-23 responsive and non-responsive individuals. We analyzed unstimulated and IL-23 stimulated FACS sorted CD8+CD45RO+ memory T cells from two individuals demonstrating robust IL-23 responsiveness, and two individuals demonstrating low IL-23 responsiveness, using the Affymetrix Human Exon 1.0 ST platform. Array data was processed by Affymetrix Expression Console software. No techinical replicates were performed.