Nickel subsulfide (Ni3S2), nickel sulfate (NiSO4), nickel chloride (NiCl2), and nickel oxide (NiO), are four compounds encountered by workers in the nickel‐refining and electroplating industries. These compounds were tested for their relative toxicity to beagle dog and F344/Crl rat alveolar macrophages in vitro. Dog alveolar macrophages were at least 10 times more sensitive to the effects of each of the 4 nickel compounds than were rat alveolar macrophages. Toxicity ranking of the four nickel compounds to macrophages from both species was Ni3S2> NiCl2∼ NiSO4> NiO.