We report here a comprehensive evaluation of the effects of culture duration on the gene expression of P450 isoforms, uptake transporters and efflux transporters in human hepatocyte cultured in the absence and presence of the prototypical proinflammatory cytokine, interleukin-6 (IL-6). Primary collagen-matrigel sandwich cultures of human hepatocytes were cultured in supplemented William's E medium containing 0, 0.1, 0.5 and 5 ng/mL of IL-6 for the time periods of 2, 6, 12, 24 and 48 hrs. Real-time PCR was performed to quantify gene expression of acute phase proteins (suppressor of cytokine signaling 3 (SOCS-3), c-reactive protein (CRP) and lipopolysaccharide (LPS)-binding proteins (LBP)); P450 isoforms (CYPs 1A2, 2B6, 2C8, 2C9, 2D6, 3A4, and 3A5), uptake transporters (SLC10A1, SLC22A1, SLC22A7, SLCO1B1, SLCO1B3, SLCO2B1) and efflux transporters (ABCB1, ABCB11, ABCC2, ABCC3, ABCC4, ABCG2). SOCS-3, CRP, and LBP were extensively induced by IL-6, with maximal induction observed at 2 (SOCS-3) and 12 hrs (CRP; LBP), demonstrating that the cultured human hepatocytes responded to IL-6 treatment. In the untreated group (control), gene expression of P450 isoforms and uptake transporters decreased while efflux transporters remained relatively stable or increased with cultured duration. IL-6 predominantly caused down regulations of the genes studied, with the most significant changes observed at different treatment durations, apparently related to the stability of the basal levels of gene expression. For instance, for genes with unstable expression, which would decrease rapidly in culture (e.g CYP3A4), the most definitive down regulatory effects were observed at a relatively early time point (e.g. 12 hrs). In contrast, a longer treatment duration (e.g. 48 hrs) was required for genes with relatively stable expression levels in culture (e.g. ABCB1). Based on our findings, evaluation of multiple treatment durations rather than single treatment duration is recommended for the evaluation of biotherapeutics in cultured human hepatocytes where down regulation is expected.