Pools of 26S and 20S proteasomes were studied in the spleen, liver, lung, and ascitic carcinoma Krebs-II of mouse. Western blotting demonstrated that the pool of 26S proteasomes in ascitic carcinoma Krebs-II was twice that in control lung cells and did not significantly differ by total 26S proteasome quantities from the spleen and liver. At the same time, the level of immune subunit LMP7 was 12 times lower in it compared to lung proteasomes and 4-5 times lower compared to spleen and liver proteasomes. Immune subunit LMP2 was undetectable by this technique in the ascitic carcinoma in contrast to the lung, spleen, and liver. All immune subunits in the studied organs and ascitic carcinoma Krebs-II are components of 26S but not 20S proteasomes.