Ten cohorts of nickel exposed workers which had previously been studied in terms of total nickel exposure were updated and re-analyzed to evaluate the cancer risk from the various chemical forms of nickel to which they had been exposed. Industrial records were used to construct occupational histories of individual workers and to derive estimates of exposure to nickel and its compounds in their working environments. Subsequent mortality was then assessed in relation to exposure estimates. The major conclusion from the research is that risk to lung and nasal cancer is related to more than one form of nickel. Although increased risk in most workers can be attributed to mixtures of oxidic and sulfidic nickel, high exposures to nickel oxide in the absence of nickel subsulfide was also associated with increased risk. There was also evidence that soluble nickel increases cancer risk.