The three general principles of the International Commission on Radiological Protection (ICRP) are: justification, optimisation (ALARA) and dose limitation. The principle application of optimisation (ALARA) for occupational exposures of workers or the public to external radiation is reliant on low doses being assessed accurately, which could be achieved using biological dosimetry. Although cytogenetic analyses for dicentrics and translocations are the most useful techniques for biological dosimetry, these were initially developed for and have been applied to middle and high range dose exposures; the range where deterministic injury is possible. Application of these techniques for biomonitoring or screening of relatively large groups of low exposed people is possible but limited as chromosome analysis is time-consuming and requires highly skilled personnel. In addition, some technical considerations constrain dose estimation in the low dose range. This paper considers the advantages of cytogenetic techniques for biodosimetry and also highlights their limitation at low doses. However, optimisation of low dose assessment could be obtained by improvement in the technique perhaps in combination with other approaches that consider variations in individual sensitivity. Developments in modern molecular biology have brought new approaches into prospect but so far they are not routinely applicable. The potential use and throughput of these new technologies is discussed.