IL-1β and H2O2 induce the expression of HIF-1α mRNA in human articular chondrocytes. Under normoxic culture conditions, mRNA levels of hypoxia-inducible factor 1α (HIF-1α) were observed in cultured chondrocytes, whereas HIF-1α protein was undetected in the cells. HIF-1α mRNA was accelerated by IL-1β or H2O2 in cultured chondrocytes under hypoxic conditions. Cobalt chloride (CoCl2), chemical inducer of HIF-1, was used for the positive control. *P < 0.05, **P < 0.01 compared with the control. Cont., control.