Radiolabelled (3H-labelled) Antineoplaston A10 was administered in a single dose of 220 mg to 230 mg/kg to female Sprague Dawley rats. Blood and urine samples for determination of radioactivity were collected one hour prior to, and then at different time intervals after, the administration of the drug. Rats were sacrificed 6 h or 36 h later for the study of radioactivity in the various organs. The concentration of radioactivity in blood reached a maximum after 2 to 3 h after the administration of Antineoplaston A10, whereas the highest concentration of radioactivity in urine was observed in the 3.5-h to 4-h samples. It was observed by quantitative HPLC analysis that in rats sacrificed 6 h after Antineoplaston A10 administration, between 61% to 69% of the drug was absorbed, whereas between 37% to 28% was found in the stomach and between 2% to 3% was present in the intestinal contents and faeces. After 36 h, none could be detected in the stomach, intestinal contents or faeces. Organ distribution studies indicated greater accumulation of radioactivity in ileum, bladder, duodenum, kidneys and jejunum, and relatively low accumulation in the heart, lung, liver and brain. The concentration of radioactivity after 36 h was very low. By quantitative measurement, between 40% to 42% of the drug was excreted in the urine in 6 h and 75% of the radioactive material was in the form of Antineoplaston A10. The identification of the major radioactive material as Antineoplaston A10 was confirmed by TLC and analysis of the products of acid hydrolysis and by determination of melting range.