The main concern of operational internal dosimetry is to detect intakes and estimate doses to the worker from a series of bioassay measurements. Although several methods are available, the inverse problem of internal dosimetry—i.e., determination of time, amount, and types of intake given a set of bioassay data—is well suited to a Bayesian approach. This paper summarizes the Bayesian methodology used at Los Alamos National Laboratory to detect intakes and estimate doses from plutonium bioassay measurements. Some advantages and disadvantages of the method are also discussed. The successful application of Bayesian methods for several years at Los Alamos National Laboratory, which monitors thousands of workers annually for plutonium, indicates that the methods can be extended to other facilities.