Rabbits were exposed to soluble nickel chloride, about 0.3 mg/m3 as nickel, for about 1 month (5 days/week, 6 hr/day). The upper lobe in the left lung was examined with light microscopy and samples from the left lower lobe with electron microscopy. Nodular accumulation of macrophages and laminated structures occurred in alveoli of all exposed rabbits, but otherwise no inflammatory reactions. Volume density of the alveolar epithelial type II cells was doubled due to increased cell number as well as cell volume. The tissue content of phospholipids, determined in the lower lobe of the left lung, had increased by about 40%, mainly due to elevated disaturated phosphatidylcholines. The effect pattern was almost identical to that seen earlier in inhalation experiments with metallic nickel dust, strongly indicating that nickel ions are responsible also for the changes seen after exposure to metallic nickel. This suggests that all nickel compounds may produce the pathological condition, which is similar to that seen in the disease pulmonary alveolar proteinosis.