Comparison of the relative HIF-1α mRNA expression ratio of SW480 and SW620 cell lines between normoxia and hypoxia conditions. The results showed that the relative HIF-1α mRNA expression levels were elevated in cells exposed to hypoxia conditions. The relative HIF-1α mRNA expression ratio of SW480 cell lines were 1.26-fold (hypoxia/normoxia: 1.36/1.08; after 24 h incubation) and 2.63-fold (hypoxia/normoxia: 6.37/2.42; after 48 h incubation); however, there was a 1.43-fold (hypoxia/normoxia: 1.76/1.23; after 24 h incubation) and 3.32-fold elevated HIF-1α mRNA expression (hypoxia/normoxia: 7.63/2.30; after 48 h incubation) in SW620 cell lines. The control groups were incubated in humidified atmospheric air without the addition of CO2. Values shown are means ± SD of 3 independent experiments with triplicate specimens.