Exposure to beryllium results in beryllium sensitization, or development of a beryllium-specific, cell-mediated immune response, in 2% to 19% of exposed individuals. Sensitization usually precedes the development of the scarring lung disease, chronic beryllium disease. The development of granulomatous inflammation in patients with CBD is associated with the production of numerous inflammatory cytokines, including IFN-gamma, IL-2, and TNF-alpha (see Fig. 1). In some individuals this can result in increased granulomatous inflammation and a more severe form of the disease. Although the exposure response relationship in sensitization and disease is nonlinear, in some studies, higher exposures were associated with higher rates of sensitization and CBD. Machinists usually have higher levels of beryllium exposure and increased risk of developing sensitization and disease. The impact of the physicochemical properties of beryllium, such as form, solubility, and particle size, on the risk of sensitization and disease are less well understood. It is clear from numerous studies that genetic susceptibility affects risk of beryllium-related health effects. The role of HLA-DPB1 Glu69 in the proliferative response to beryllium and risk of sensitization has been the most well-studied. Some genes, such as Glu69, are important in the development of an antigen-specific, cell-mediated immune response to beryllium or sensitization, whereas others may be important in the development of beryllium-specific granulomatous inflammation or CBD (see Fig. 1). Two copies of the Glu69 gene may be a disease-specific genetic risk factor. The TNF-alpha -308 A variant is associated with beryllium-stimulated TNF-alpha production, which, in turn, is associated with more severe CBD. Whether the TNF-alpha -308 A is a genetic risk factor in CBD, sensitization, or more severe disease still needs to be determined. It is likely that sensitization and CBD are multigenetic processes, and that these genes interact with exposure to determine risk of disease. Current genetic markers are not ready for clinical use as a screening test for beryllium-related health effects because of the low specificity of the markers and the low prevalence of BeS and CBD.