The interleukin-23 (IL-23) pathway, T helper 17 (Th17) cells and γδ T cells, which respond to IL-23, have major pro-inflammatory roles. We have used unique IL-23 receptor (IL-23R) subunit-specific monoclonal antibodies, X67 and X68, and IL-12 receptor beta-1 subunit (IL-12Rβ1) expression levels to evaluate the IL-23R complex on CD4 β TCR Th17 cells and on γδ T cells. Both IL-23R and IL-12Rβ1 subunits constitute the functional IL-23R. Expression of the IL-23R subunit by cultured Th17 cells was heterogeneous. Th17 cells expressed consistent high levels of the IL-12Rβ1 subunit, which appeared a better predictor of responsiveness to IL-23 than the expression of the IL-23R subunit. Moreover, sorting memory CD4 T cells by high IL-12Rβ1 expression selectively enriched cells committed to IL-17 production from the blood. IL-23R expression was also observed on freshly isolated and cultured γδ T cells and the cultured γδ T cells were not responsive to IL-23.