To obtain information for more detailed studies of how rice responds to climate change, plants of three high tillering (IR30, IR52, IR74) and two low tillering cultivars (Azucena and IRAT 104) were grown under controlled environment conditions for 28 days. Across all rice cultivars, a 300microL/L increase in CO2 simulated root growth more than shoot growth, but neither leaf nor stem weight and leaf or tiller number was affected by CO2. In contrast, increasing temperature of 6C for 28/22C stimulated shoot but inhibited root growth, resulting in a significant increase (38 to 69%) in leaf number but a significant decrease (32 to 48%) in root/shoot ratio and nonsignificant changes for other parameters. Cultivars responded similarly to CO2 or temperature; there were no significant CO2 x cultivar or temperature x cultivar interactions. However, rice cultivars responded differently to the same environment; IRAT 104 plants tended to have lower dry weights and tiller numbers than the IR cultivars with Azucena as intermediate. Azucena had lower root/shoot ratios than the other cultivars.