We report the synthesis and characterisation of the nitroxide spin-labelled photoactivatable Pt(iv) prodrug trans,trans,trans-[Pt(N3)2(OH)(OCOCH2CH2CONH-TEMPO)(Py)2] (Pt-TEMPO, where TEMPO = 2,2,6,6-tetramethylpiperidine 1-oxyl). Irradiation with blue visible light gave rise to Pt(ii) and azidyl as well as nitroxyl radicals. Pt-TEMPO exhibited low toxicity in the dark, but on photoactivation was as active towards human ovarian cancer cells as the clinical photosensitizer chlorpromazine and much more active than the anticancer drug cisplatin under the conditions used.