The most important risk factors for the development of carboplatin-induced thrombocytopenia are total dose, glomerular filtration rate (GFR) and pre-infusion platelet count (P0). Pharmacokinetic and toxicity data from 23 patients with ovarian or testicular cancer were combined with published values from four other centers and the relationships between plasma clearance of ultrafilterable platinum and GFR, and between percentage reduction in platelet count and area under the plasma platinum curve were determined. The scatter in the data was estimated and used in a Monte-Carlo computer simulation to derive the following five-level dosing scheme. [table: see text] The scheme is based on 5% of patients incurring grade IV thrombocytopenia. Using this scheme, the majority of patients with ovarian or testicular cancer receiving carboplatin will be given an initial dose of 900 mg.