Background: Phenoxodiol is a novel isoflavone currently being studied in clinical trials for the treatment of cancer. This study reports the pharmacokinetics of phenoxodiol in patients with cancer. Methods: The pharmacokinetics of phenoxodiol was studied following a single intravenous (iv) bolus dose and during a continuous intravenous infusion. Three men with prostate cancer and 3 women with breast cancer received IV bolus phenoxodiol (5 mg/kg) and plasma was sampled for free and total phenoxodiol levels. On a separate occasion 5 of the same patients received a continuous intravenous infusion of phenoxodiol (2 mg/kg/h) and plasma was again sampled for free and total phenoxodiol levels. Phenoxodiol was measured using gradient HPLC with ultraviolet detection. Results: Following bolus injection, free and total phenoxodiol appeared to follow first order pharmacokinetics. The elimination half-lives for free and total phenoxodiol were 0.67 ᠰ.53 h and 3.19 ᠱ.93 h, respectively, while the total plasma clearance rates were 2.48 ᠲ.33 L/h and 0.15 ᠰ.08 L/h, respectively. The respective apparent volumes of distribution were 1.55 ᠰ.69 L/kg and 0.64 ᠰ.51 L/kg. During continuous intravenous infusion, free phenoxodiol accumulated rapidly to reach a mean concentration at steady state of 0.79 ᠰ.14 姯ml after 0.87 ፊ0.18 h. The apparent accumulation half-life of free phenoxodiol was 0.17 ᠰ.04 h while the plasma clearance during continuous infusion was 1.29 ᠰ.23 L/h. Conclusions: Phenoxodiol has a short plasma half-life, particularly in the free form, leading to a rapid attainment of steady state levels during continuous intravenous infusion.