A degradation pathway for carboplatin in aqueous solution is described. Degraded solutions of carboplatin in water and in 5% glucose solution were analysed by high performance liquid chromatography; carboplatin and its degradation products were well separated. Three degradation products of carboplatin have been determined either in pure water and 5% glucose solution and they have been identified as 1,1-cyclobutanedicarboxilate anion, its protonated forms and cis-diamminediaquoplatinum (II) complex.