Far infrared radiation has excellent radiation characteristics and high energy conversion rates can be achieved using ceramic coated radiators. Using such a radiator, the dehydrating synergy, generated by far infrared radiation heating under vacuum condition, the drying of welsh onion was studied. The radiation intensity levels influenced dramatically the drying rate and the product qualities: the a* for rehydrated onions, and the L* and DeltaE(ab)(*) for dehydrated onions. A rising-rate period, a constant-rate period, and a falling-rate period were ascribed to the drying behaviour. The radiation also had significant effects on chlorophyll content. The long time in drying and the high temperature may have contributed to a decrease in rehydration properties. (C) 2002 Elsevier Science Ltd. All rights reserved.