Cis-Diamminedichloroplatinum(II) is an antineoplastic drug that is undergoing a renewed clinical interest as a drug for use in combination regimens. To increase the understanding of the pharmacokinetics of this drug, the plasma clearance and organ distribution of Pt were followed in female beagle dogs treated with a single i.v. dose of cis-diamminedichloroplatinum(II). Plasma levels of Pt were determined by flameless atomic absorption spectrometry and showed a distinctly biphasic clearance pattern with a rapid-phase half-time of considerably less than 1 h and a slow-phase half-time of nearly 5 days. During the first 4 h after treatment plasma levels fell by 90%, while 60-70% of the applied dose was recovered in the urine. Sixteen tissues plus plasma, bile and urine were routinely analyzed for Pt content. An easily measurable plasma concentration of Pt was still detectable 12 days after treatment, with no significant change in plasma concentration between days 4 and 12. Initial concentrations of Pt were highest in organs of excretion, gonads, spleen and adrenals but remained significantly elevated only in kidney, liver, ovary and uterus, where a tissue plasma ratio of 3:4 was maintained for as long as 6 days post-treatment. The apparent in vitro binding of Pt to dog plasma and bovine serum albumin was studied by ultrafiltration and increased progressively during 48 h of incubation at 37.degree. C.