Experience with bioassay for tritium has been obtained during a 2-yr period. Occupationally exposed persons involved in this surveillance represent three types of exposure approximately described by International Commission on Radiological Protection models for continuous, recurrent, and single intake. The results show that, under special conditions—for instance, at a research reactor or in laboratories where tritium sources with known release rates are used—urinalysis with less frequency is sufficient. For single or recurrent intake encountered in the production of labeled compounds or during maintenance work in nuclear power plant installations, it has been confirmed that monthly urine sampling normally provides enough protection to the workers.