[en] Evaluation of the degree of internal radiation hazard requires knowledge of the parameters of Kr-85 metabolism in human beings. Data on the rate of saturation and desaturation of the body tissues are required for this estimation. The object of this in vivo study was to characterize the metabolism of inhaled Kr. For this purpose, measurements were made of the distribution and clearance of Kr following inhalation of ⁷⁹Kr by the normal subjects. The rate constants determined for ⁷⁹Kr were used to calculate the radiation dose associated with exposure to the long-lived ⁸⁵Kr. The retention data were obtained with the Brookhaven whole-body counter. The clearance of ⁷⁹Kr from the body indicates five components ranging in half-times from 14 sec to 9.6 h. The slowest components, varying between 4.2 and 9.6 h, correlated highly with percent body fat. The long-term retention was localized in regions of high fat content. The stimated radiation dose based on the retention data of this study indicates that doses to body fat and gonads are larger than those estimated by other investigators. This increased estimated dose derives from the increase in retention time of krypton in fat pools