The in vivo distribution in man of the four platinum derivatives cis-dichlorodiammine platinum(II) (DDP), cis-trans-dichlorodihydroxy-bis-(isopropylamine) platinum (IV) (CHIP), cis-dichloro-bis-cyclopropylamine platinum(II) (CP), and cis-diammine 1, 1-cyclobutanedicarboxylate platinum(II) (CBDCA) has been observed. The availability of these compounds labelled with the radioactive isotope of platinum, platinum-191, has made serial in vivo imaging of their distribution possible. Injection of 17-35 MBq (5-28 mg) of the labelled compound IV was followed by imaging, using a gamma camera, with particular reference to the kidneys, liver, and tumour site. Hepatic and renal clearances were observed in all nine patients, but no unequivocal evidence of tumour uptake was found. The left kidney uptake was estimated at times up to 7 days after injection. Mathematical analysis of some of the uptake curves failed to show any significant difference between the clearance times observed. However, the two patients who received CBDCA did show a higher initial renal uptake, falling within the 1st day to levels comparable with those of the other compounds, and the three patients who received DDP showed consistently liver uptake.