This study addresses the effects of low-level alpha-radiation on bioluminescent assay systems of different levels of organization: in vivo and in vitro. Three bioluminescent assay systems are used: intact bacteria, lyophilized bacteria, and bioluminescent system of coupled enzyme reactions. Solutions of 241Am(NO3)3 are used as a source of alpha-radiation. It has been shown that activation processes predominate in all the three bioluminescent assay systems subjected to short-term exposure (20-55 h) and inhibition processes in the systems subjected to longer-term exposure to radiation. It has been found that these effects are caused by the radiation component of 241Am3+ impact. The intensity of the 241Am3+ effect on the bioluminescent assay systems has been shown to depend on the 241Am3+ concentration, level of organization and integrity of the bioluminescent assay system. The bioluminescent assay systems in vivo have been found to be highly sensitive to 241Am3+ (up to 10(-17) M).