Lipase from Candida rugosa was stabilized against thermal inactivation in the presence of polyvinylalcohols (PVA) of different molecular weights. The apparent rate constant of the lipase inactivation, k(d), at 49 degrees C is 0.049/min and a 0.022/min in the absence and in the presence of PVA (mol wt 22,000), respectively. The improvement of the lipase thermostability by adding PVA was confirmed by differential scanning calorimetry. The presence of PVA had also an effect on the hydrolytic activity of the enzyme. Furthermore, lipase was modified by covalent linkage to PVA by means of an original procedure. With respect to the native enzyme, the modified lipase has a slightly lower specific activity, but it is more stable against heat denaturation (k(d) 0.032/min at 49 degrees C).