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In an emerging field of nanotechnologies, assessment of exposure is an integral component of occupational and environmental epidemiology, risk assessment and management, as well as regulatory actions. This review focuses occupational exposure to carbon nanotubes (CNT).PubMed and Scopus databases were searched for period 2000–2017 using all keywords combinations based on the following structure: ‘assessment’ and ‘exposure’ and ‘carbon nanotube’. The words ‘assessment’ and ‘exposure’ were alternatively replaced by ‘measurement’ and by ‘human’ and ‘occupational’, respectively. The word ‘carbon nanotube’ was alternatively replaced by ‘single-walled carbon nanotube’, ‘double-walled carbon nanotube’, ‘multi-walled carbon nanotube’, and their abbreviations. Only field-studies conducted in occupational settings were included. The quality of the exposure measurement protocol and results reporting were reviewed. The results were compared with the current NIOSH recommended exposure limit (REL) of 1 µg/m3 respirable elemental carbon (EC) mass-concentration as an 8 hour time-weighted average.Twenty-five studies conducted in R and D laboratories, small-scale pilot-production facilities, and, more rarely, large-scale primary or secondary manufacturer/user facilities in the USA (eleven), the Republic of Korea (four), Japan (four), Russia (one) and Europe (four) were reviewed. Open handling of CNT powder during the sieving, mechanical work-up, packaging, and clean-up work-tasks was classified at highest likelihood of exposure. Fourteen most recent studies measured EC concentration, although using different methods and aerosol fractions. All but one studies observed EC values exceeding the REL. The quantification of CNT agglomerates and/or CNT-contained particles lacks methodological standardisation and precluded any comparison of results.Currently available occupational-exposure data are limited, because production and use of CNT are relatively recent and workforce sizes remain small. Due to high variability of methods and instruments used for exposure sampling and analysis and of criteria used for interpreting their results, results are difficult to compare. Further effort of methodological standardisation is warranted.