Cisplatin (cis-diamminedichloroplatinum(II») is widely used in the treatment of testicular and ovarian cancers. A number of biological and biochemical results indicate that the reaction of cisplatin with DNA is responsible for the cytotoxic action of this drug. The effect of platinum compounds on the conformation and stability of DNA has been investigated and several platinum-DNA adducts have been identified in vitro and in vivo. Preliminary experiments have quantified the effect of these different lesions on DNA replication, their capacity to induce mutations and their susceptibility to DNA repair processes. Additional DNA damage may be created by platinum(IV) compounds, perhaps during their reduction to platinum(II) compounds by the cell.