The 14C concentration in the collagen of human teeth was retrospectively investigated to determine whether its incorporation was related to atmospheric testing of nuclear weapons. Teeth were extracted for dental therapy from July 1987 to February 1988 from patients who were residents in Japan. Tooth collagen was extracted with HCl and converted to amorphous C by heating in a vacuum line. Specimens for 14C analysis were prepared by mixing the amorphous C with silver powder. The 14C concentration was measured by mass spectrometer. The 14C concentration in tooth collagen rapidly increased in 1961 after the bomb tests, peaked around 1967-1968, and then gradually decreased. The collagen of human teeth maintains the 14C concentration at the age of root completion for life. The results of this study indicate that the history of environmental contamination from atmospheric nuclear weapon's tests has been characterized by deposition of 14C in the tooth collagen 14C of human beings.