[Factors affecting 3H-thymidine incorporation into cells synthesizing DNA]

Potential sources of errors in 3H-thymidine use in cell proliferation studies are reviewed. Many factors affect the uptake of this agent into newly synthesized DNA: predominance of denovo and salvage pathways of thymidilate biosynthesis, activity of certain enzymes, size of thymidilate and TTP endogenous pools, differences in 3H-thymidine utilization rate during S-period, its catabolism in cell and tissue culture systems, degradation by bacteria, its reutilization in vivo and in vitro, effects of the isotope activity, of the exposition time of autoradiographs and of the beta-particles absorbance in the specimen. Practical recommendations are given to avoid these errors.