PURPOSE: To detect a mutagen by using cultured hepatic cells and measuring the intensity of the extremely weak light emitted by a test sample.

CONSTITUTION: A benzpyrene which is confirmed to have the carcinogenicity is used as the mutagen and a rat is used as an experimental animal. The hepatic cells thereof are collected, separated and cultured. The extremely slight light emitted by the same is measured. As a result, the extremely slight emitted light is stronger as the concn. of the benzpyrene is higher, thus the benzpyrene can be detected even if the concn. thereof is extremely low. The light emission pattern is admitted to attain a peak after several minutes. The result similar to the result of the benzpyrene is obtd. with TripP-1 as well. The mutagen is thus detected according to the above-mentioned method.