A clinically useful method is described for the quantitative analysis of platinum species derived from cis-dichlorodiammineplatinum(II) in urine. The drug and its biodegradation products are derivatized directly in urine by reaction with sodium diethyldithiocarbamate (DDTC) to form a common product, a 2:1 DDTC-platinum adduct. This complex is stable and can be quantitatively extracted into 0.1 volumes of chloroform. An aliquot of the chloroform layer is then subjected to high-performance liquid chromatography on a muBondapak CN column and the eluent monitored spectrophotometrically at 254 nm. At this wavelength the DDTC-platinum adduct has a molar absorptivity of 43,000, and platinum levels of 25 ng/ml or urine can be detected with a precision of +/- 2.5% and an accuracy of +/- 4%.