Beryllium is a rare metal but highly toxic when inhaled. The unusual properties of hardness, light weight, resistance to corrosion, high electrical and thermal conductivity, ability to form strong stable alloys and heat tolerance render beryllium of great value in a wide variety of industries. Occupational inhalation of beryllium dust is a cause of respiratory distress, chronic beryllium disease and possibly lung cancer. Beryllium is a strong sensitising agent and exposure commonly leads to multi-system granulomas. It is identified principally as a pulmonary carcinogen on the basis of sufficient clinical evidence and experimental studies in several species of animal. Beryllium is shown to be a weak mutagen in most bacterial tests, but it is cytotoxic and inhibits metabolic enzymes and has been shown to block cells in the G0–G1 pre-S phase of the cell cycle. Beryllium does occur in cigarette tobacco and despite adjustments made in statistical analyses, this complicates epidemiological study. It is notable that most epidemiological studies were completed before 1980 and reservations are expressed on the reliability of predictions made from clinical appraisals alone. Test methodology, environmental quality evaluation, worker records and job specifications, adjustments for smoking and statistical appraisals are seriously questioned.