Kinetics of conversion of ergosterol to vitamin D, has been investigated in cultivated edible mushrooms. it was observed that the rates of conversion of ergosterol to vitamin D-2 were varied in different types of mushrooms. Oyster mushrooms (Pleurotits ostreatus) showed the highest conversion rate followed by Shiitake (Lentinula edodes) and Abalone (Pleurotus cystidus) whereas the lowest conversion rate was observed in Button mushrooms (Agaricus bisporus). Both initial moisture content and temperature of irradiation influenced the conversion of ergosterol, and a 2 x 2 factorial design was used to study this influence. It was shown that the conversion of ergosterol to vitamin D, followed zero-order kinetics, where the rate constant varied with temperature according to the Arrhenius equation (K-0 = 7.32 s(-1); E-a = 51.5 kJ mol(-1)). Vitamin D-2 yields from Shiitake mushrooms with respect to temperature of irradiation (T) and moisture content of the mushrooms (M) can be calculated from the equation: D-2 = -91.3 + 2.25 * T + 71 * M. (c) 2006 Published by Elsevier Ltd.