Among the different analytical methods used for the determination of platinum in blood plasma from patients treated by platinum derivatives, inductively coupled plasma mass spectrometry appears to be the most sensitive (detection limit 0.05 microgram l-1) and the best adapted for measuring low concentrations. The preparation of the samples consisted only of a dilution. The recoveries were close to 100% and both within-run and between-days reproducibility were very good. The determination of free platinum which was only about 5% of total plasma platinum was chosen to illustrate the inductively coupled mass spectrometric method.