Effects of pretreatment and drying conditions on yam varieties, namely Dioscorea alata and Dioscorea rotundata, in a fabricated laboratory scale hot air drier at temperature range of 50-80 degrees C and constant air velocity of 1.5 m(2)/s were investigated. Mass transfer during air-drying of yam slices was described using Fick's diffusion model. Drying took place entirely in the falling rate period. Temperature dependency of moisture on diffusivity was illustrated by the Arrhenius relationship. Over the range of temperature, moisture diffusivities varied from 9.92 x 10(-8) to 1.02 x 10(-7) and 0.829 x 10(-6) to 1.298 x 10(-5) m(2)/s for D. alata and D. rotundata, respectively. Activation energy for drying of D. alata and D. rotundata varied from 25.25 to 46.46 and 41.75 to 72.47 kJ/mol, respectively. (c) 2006 Elsevier Ltd. All rights reserved.