The production of cytokines can be controlled by the regulation of transcription, by the regulation of translation, and by post-translational mechanisms. Therefore, to understand better the control of cytokine production, it is important to measure both concentration of the free cytokine in solution and cytokine mRNA in the cytokine-expressing cells. Traditional methods of examining gene expression, such as as Northern blots, reverse transcriptase polymerase chain reaction (RT-PCR), and RPA, tend to be labor intensive and semiquantitative. To overcome these limitations, we have developed the Xplore� (Endogen, Woburn, MA) assay for the quantification of cytokine mRNA. These microtiter plate-based assays are rapid (under 6 h), quantitative over three orders of magnitude, and have no risk of falsepositive values from contamination.