Carcinogenic activity of particulate nickel compounds is proportional to their cellular uptake.

Particles (less than or equal to 5 micrometers) of the potent carcinogen crystalline nickel subsulfide were actively phagocytized by cultures of Syrian hamster embryo cells and Chinese hamster ovary cells. Cells did not take up significant quantities of similar-sized particles of the noncarcinogen amorphous nickel monosulfide. The carcinogenic activity of this and other metal compounds appears to be proportional to their cellular uptake.