The potential internal occupational exposure encountered as a consequence of the 232Th-233U fuel cycle are likely to arise predominantly from the inhalation of 232Th, 233U and (232Th + 233U) compounds of absorption Types M and S. In the past, although direct and indirect methods for assessments of internal exposure to 232Th and its daughters were developed, standardised and employed, no such attempts have been made with regard to 233U and 233U + 232Th. Therefore, feasibility studies for assessing internal exposure to 233U have been conducted using three methods: urine bioassay, in vivo counting and measurement of thoron gas in the exhaled breath of a worker. This paper describes details of these studies and discusses the results obtained.