Beryllium is a light-weight metallic element, which was first recognized as a lung hazard in Europe in the 1930s, shortly after its first production in modern industry. People exposed to beryllium compounds are at increased risk of developing beryllium sensitization and chronic beryllium disease (CBD). The chronic lung disease was first described among workers exposed to beryllium-containing materials used in the manufacture of fluorescent lamps. In primary production of beryllium metal, which was used in nuclear weapons components, physicians recognized severe dermatitis, reversible pneumonitis, and chronic granulomatous lung disease. Physiologically, this metal/element exists as an ion in the body. It is now recognized that the physicochemical properties of beryllium compounds may account for the differing clinical presentations in different industries. In primary production of beryllium metal, soluble salts are present and cause rashes in approximately one fourth of exposed workers and reversible acute pneumonitis in a smaller portion of the workforce. After heavy inhalation exposures, radiographic abnormalities evolve at approximately three weeks; resolution of symptoms and radiologic abnormalities away from exposure occur only after months, but symptoms recur immediately upon reexposure. The granulomatous nature of chronic beryllium disease is now known to be caused by cell-mediated sensitization to beryllium. Chronic beryllium disease (CBD) is a granulomatous lung disorder characterized by the accumulation of beryllium-specific CD4(+) T cells. Depending on genetic susceptibility and the nature of the exposure, CBD occurs in up to 20% of exposed workers. Genetic susceptibility has been associated with particular HLA-DP alleles, especially those possessing a negatively charged glutamic acid residue at the 69th position of the beta-chain. The mechanism for this association lies in the ability of these HLA-DP molecules to bind and present beryllium to pathogenic CD4(+) T cells. Large numbers of effector memory, beryllium-specific CD4(+) T cells are recruited to the lung of these subjects and secrete Th1-type cytokines upon beryllium recognition. The presence of circulating beryllium-specific CD4(+) T cells directly correlates with the severity of lymphocytic alveolitis. Since 1987, this biomarker of sensitization has enabled medical surveillance of beryllium-exposed workforces. Beryllium lymphocyte proliferation tests have been used to screen workers to detect sensitization, to characterize epidemiologically workplace risks for beryllium sensitization, and to evaluate the effectiveness of interventions intended to prevent sensitization. The most compelling real-world example of genetic testing for susceptibility to a workplace exposure involves those industries that process or fabricate beryllium. Under reasonable assumptions, the longitudinal positive predictive value of the HLA-DPB1-Glu69 marker of susceptibility to beryllium disease is 12%. Interpretive challenges further limit the utility of the test and may inadvertently suggest a false sense of safety among workers. Reduction in inhalation exposure to beryllium has not resulted in a concomitant reduction in the occurrence of beryllium sensitization or CBD, suggesting that continued prevalence may be due, in part, to unchecked skin exposure to beryllium-containing particles. (PMID: 17094767, 16697706, 16231190).