Hypoxia modulates collagenase expression by rheumatoid arthritis synovial cells. Rheumatoid arthritis synovial cells were exposed to either 21% oxygen (normoxia) or 1% oxygen (hypoxia) for 24 hours. mRNA levels of (a) matrix metalloproteinase (MMP)-8 and (c) MMP-13 were measured by quantitative PCR (n = 10 to 14). The change in threshold cycle (ΔCt) values was calculated for each mRNA using the 2-ΔΔCt method against the housekeeping gene acidic ribosomal protein. The fold changes in mRNA levels were related to a reference sample (human cDNA). In parallel, release of (b) MMP-8 and (d) MMP-13 protein was measured by ELISA of cell culture supernatants (n = 12 to 13). Data were analysed versus normoxia by Wilcoxon signed rank test: *P < 0.05, **P < 0.01.