The serum immunoglobulin levels, ribosome contents and protein synthesis rate in peripheral blood lymphocytes have been studied in 35 patients with chronic lymphatic leukemia. It is shown that in patients whose lymphocyte ribosome content corresponds to that of the donors IgG, IgA, IgM levels were on the average normal whereas in the patients with the decreased ribosome content IgG and IgA were 2-2.7 times lower, while the IgM concentration was normal. Hypogammaglobulinemia of IgG, IgA and IgM types in 47% of patients with the normal ribosome contents was 23%, 29% and 23%, respectively, and in 100% of patients with the low ribosome content it was 72%, 83% and 68%, respectively. There was no distinct correlation between the immunoglobulin levels and the protein synthesis rate. The ribosome pattern in the lymphocyte maturation in chronic lymphatic leukemia is discussed.