genicity of silica. The Working Group concluded that "crystalline silica inhaled in the form of quartz or cristobalite from occupational sources is carcinogenic to humans (group 1)" classification for crystalline silica was reached largely as a result of some very supportive findings from individual studies. However, there were some studies that did not demonstrate lung cancer excesses, and the IARC conclusion remains somewhat controversial 12. Exposure-response trends were not always consistent in studies in which such analyses had been done. Furthermore, exposure