Exact equations for the experimental analysis of fission-gas holdup beds are developed by the method of statistical moments. The mean retention time, given by the first moment, is independent of the factors which affect mass transfer. This independence emphasizes the important fact, sometimes overlooked in the analysis of fission-gas holdup beds, that the true dynamic adsorption coefficient for a stable fission-gas isotope is identical to the static adsorption coefficient. The second moment, used in combination with the first moment, describes the spreading of the input after it has passed through the holdup bed. The meaning of these equations is examined in detail, and by their correct use the factors needed for the design of fission-gas holdup beds can be determined rapidly from laboratory experiments. This method of analysis is applied to data obtained from fronts of dilute 85Kr passed through charcoal beds.