This study examined the relationship between the lay judgment of carcinogenic risk threshold and attitude toward nuclear power plants. After the experimenter explained the concept of the threshold in dose-response relationship, one-hundred and thirty students gave their judgment of the threshold in the dose-response relationship of carcinogenic risk of exposure to radiation and their attitudes toward nuclear power plants. Then they watched a sensational TV program reporting on the danger of nuclear waste and its storage. After that they were given the same questions which they had answered previously. The results suggested that there was no relationship between judgment of threshold and attitude toward the nuclear power plants. Also the judgment had no relationship to the attitude change brought about by the TV program. Implications of these results for radiation risk management and communication are discussed.