[en] Results on the influence of 6 MeV electron beam and 2.45 GHz 565 W microwaves as well as of the combined treatment, at -3 deg C and -196 deg C, on lactate dehydrogenase activity are presented. The loss of enzymatic activity is significantly influenced by the temperature gradient used to lower the temperature of the samples .Our data showed a moderate inactivation of the electron irradiated lactate dehydrogenase, in the dose range (0-4.2 kGy). The microwave irradiated samples exhibited a non-linear behaviour, consisting of successive activation and inactivation of the enzyme molecules, which suggests the major influence of the nonthermal component of microwave radiation. The combined electron and microwave irradiation procedure lead to similar behaviour of the enzyme as in the case of electron irradiation, suggesting that the microwaves impact on the enzyme activity is very low, under our experimental conditions. The frozen enzyme showed a complex behaviour, because of the superposition of freeze-thawing procedure effects on the irradiation effects, both molecular mechanisms being incompletely clarified so far. (author)