The meaning and usefulness of biological indicators in the study of occupational exposure to aluminium (Al) was assessed on the basis of the most recently acquired knowledge on the toxicokinetics of aluminium absorbed by inhalation, results of environmental and biological investigations recently carried out in industrial sectors with low risk of aluminium absorption (refining, casting and pressure moulding covering a total of 8 plants and 119 workers) and the results of investigations on a group of welders exposed to Al concentrations between 5 and 10 mg/m3. It was confirmed that not only the environmental Al concentrations but also certain chemical and physical characteristics (particle size, allotropic state, solubility), simultaneous exposure to other dusts, and mode of exposure (existence of exposure peaks) play a significant role in lung absorption of Al. Urinary Al (AlU) may be considered as an indicator of "recent" exposure with biphase excretion kinetics influenced also by duration of exposure, whereas Al in serum (AlS) can probably furnish indications both on overall exposure and on body burden. In low-level Al exposure (below 0.5 mg/m3), these indicators (especially AlU) permit differentiation of the exposed groups from the general population without, however, any clear relationship with the various environmental Al concentrations. It was also seen that AlU increased with increasing work seniority and was more marked in certain processes, such as casting, and in the first few months or years of work.(ABSTRACT TRUNCATED AT 250 WORDS)