Detection of DNA fragmentation by LM-PCR in TE671, LS174T, RKO, and MCF7 cells incubated for 48 h with various concentrations of 125IdUrd. Upper panel: Left lane contains molecular weight markers. DNA-incorporated 125I activity (mBq/cell) and survival fractions are shown. Lower panel: En-2, a single-copy gene that is conserved in most species, has been run as control (same amount of DNA used).