A simple procedure is described for the determination of platinum in tumours after cisplatin therapy. Tumours were digested in 65% nitric acid by incubation at 37 degrees C for 2 days and platinum analysed under optimum conditions by electrothermal atomic absorption spectrometry with Zeeman background correction. The reproducibility of measurements in general was better than +/- 2%. The calibration graph was linear from 30.0 up to 1000 micrograms l-1 of platinum, while the limit of detection (3 sigma) was found to be 3.0 micrograms l-1 (sample volume 20 microliters). Aqueous standard solutions and the standard addition method were applied in the calibration procedure. Under the recommended analytical conditions, the sample matrix did not influence the determination of platinum significantly. In 72% of samples analysed the differences between results obtained by the two calibration procedures did not exceed +/- 5%.