[en] Beagles that inhaled ²³⁹PuO₂, ²³⁸PuO₂, or ²³⁹Pu(NO₃)₄, in dose-level groups of 20 dogs, with initial lung burdens of ∼2, 15, 70, 300, 1100, or 5500 nCi, are now 11, 9, or 5 years postexposure. Lung tumors, bone tumors, and radiation pneumonitis, the plutonium-exposure-related causes of death observed to date, have occurred in the two, three, and four highest dose-level groups exposed to ²³⁸PuO₂, ²³⁹Pu(NO₃)₄, and ²³⁹PuO₂, respectively. No plutonium-exposure-related deaths have thus far been observed in dose-level groups exposed to less than ∼40 times the current maximum permissible lung dose for a plutonium worker. Plutonium-exposure-related effects not directly related to the cause of death include chronic lymphopenia, chronic neutropenia, sclerosis of the tracheobronchial lymph nodes, focal radiation pneumonitis, adenomatous hyperplasia in the liver, and dystrophic osteolytic lesions in the skeleton. No plutonium-exposure-related effects have thus far been observed in dose-level groups that received less than ∼15 times the current maximum permissible lung dose for a plutonium worker. 10 refs., 5 figs., 4 tabs