Platinum was lost from the DNA of cis-diamminedichloroplatinum(II) [cis-Pt(II)]-treated exponentially growing Chinese hamster V79-379A cells with a half-life of 28 hr. By contrast, platinum was lost from the DNA of cells treated in stationary-phase culture with a half-life of 4 days. Cells treated in and allowed to remain as a stationary-phase culture maintained an intact and apparently viable appearance. When the stationary-phase culture was diluted with fresh medium, cell division occurred, and cell survival, as measured by colony-forming ability, could be determined. Dilution of cells immediately after treatment with 40 µm cis-Pt(II) resulted in 0.19% control survival. There was an increase in the ability of the stationary-phase cells to survive cis-Pt(II) damage with time after treatment. Thus, after 3 days, the survival had increased from 0.19 to 15.9%. We demonstrate that this increased ability of stationary-phase cells to survive with time after treatment is due to DNA excision repair and hence that survival is inversely related to the extent of reaction of cis-Pt(II) with the DNA.