Hypoxia differentially modulates the angiogenic balance. Rheumatoid arthritis synovial cells were exposed to either 21% oxygen (normoxia) or 1% oxygen (hypoxia) for 24 hours. mRNA levels of (a) vascular endothelial growth factor (VEGF) and (b) placental growth factor (PlGF) were measured by quantitative PCR (n = 19). 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 (c) PlGF and (d) VEGF/PlGF heterodimer was measured by ELISA of cell culture supernatants (n = 13 to 15). Data were analysed versus normoxia by Wilcoxon signed rank test: *P < 0.05, ***P < 0.001.