[en] An investigation has been made of the capabilities of cis-dichlorobis(isopropylamine)trans-dihydroxy platinum IV (CHIP) as a hypoxic-cell sensitizer, over an x-ray dose range of 0 - 16 Gy. Using single C₃H mouse mammary tumour cells with 60 μg ml^-1 (144μM) of CHIP, followed by irradiation under aerated or hypoxic conditions after different time intervals, survival of colony-forming ability was assessed after seven days' incubation at 37⁰C. CHIP appeared to have a potentiating effect over the low and high dose range under hypoxic conditions but not in air. There was a decrease in the survival level in the 'shoulder region', accompanied by a decrease in the final slope. At the one hour time-interval, the survival over the low dose range was identical with that of cells irradiated under aerated conditions. (U.K.)