Konjak (Amorphophallus konjac K. Koch) was grown under normal (350 μbar) or enriched (700 μbar) CO2 partial pressure in glasshouses kept at 33/26 °C. Doubling the CO2 partial pressure resulted in twice the yield of corm because the net CO2 assimilation rate doubled and, due to the simple source-sink relationship, the increased production was partitioned to the corm. The response to CO2 of assimilation by konjak is discussed in relation to its original habitat in the tropics.