A multicompartmental model is developed to simulate the biokinetics in the human body following the ingestion of an inert gas. It was assumed that 100% of the radon ingested appears in the stomach, from which it is transported through the body to different organs via the blood stream. Each of these organs absorbs and releases radon differently, and, amongst all, the fat retains radon for the longest time. To test the model, the information on elimination rates of 222Rn in expired breath was obtained from other experiments done at the University of Maine. The data included male and female participants with a wide range of ages and physical activity levels. The radiation doses in the different organs and tissues were computed. As was expected, the stomach sustained the maximum dose. In this study, the highest stomach dose to any volunteer was evaluated as 115 mSv y(-1).