Tritiated thymidine: effect of decomposition by self-radiolysis on specificity as a tracer for DNA synthesis.

Tritiated thymidine undergoes decomposition by self-radiolysis. As shown by beta liquid-scintillation measurement and by autoradiography, the resultant breakdown products did not label DNA, but entered macromolecules, other than nucleic acid, contained in the cytoplasm. Caution should be exercised in using aged tritiated thymidine solutions.