The stability of cisplatin, iproplatin, carboplatin, and tetraplatin in common intravenous solutions was studied. Admixtures of each drug in each of the following vehicles were prepared in glass containers: 0.9% sodium chloride injection, 5% dextrose injection, 5% dextrose and 0.9% sodium chloride injection, 5% dextrose and 0.45% sodium chloride injection (admixtures were prepared in plastic bags also), and 5% dextrose and 0.225% sodium chloride injection. Drug concentrations were monitored for 24 hours using stability-indicating high-performance liquid chromatographic methods. The stability of cisplatin and tetraplatin was related to the chloride ion content of the infusion fluid; when the infusion fluid contained 0.9% sodium chloride, each of these drugs was present at greater than 90% of the original concentration after six hours. The stability of iproplatin was not related to chloride concentration. A slight increase in the decomposition rate of carboplatin was observed in the presence of chloride ion. Carboplatin and iproplatin are stable for 24 hours in all the infusion fluids studied, but carboplatin should not be diluted with solutions containing chloride ions because of possible conversion to cisplatin. Cisplatin is stable for 24 hours in admixtures containing sodium chloride concentrations of 0.3% or greater. Tetraplatin is stable for six hours in admixtures containing sodium chloride concentrations of at least 0.018%.