Examined were 57 patients with teratomas, cysts, lymphoepithelial and malignant thymomas. One hundred donors of the blood served as a control. In the blood of the normal subjects, (0.315 +/- 0.014) X 10(9)/L of large granule-containing lymphocytes were revealed, in patients with benign tumours--(0.2 +/- 0.02) X 10(9)/L, with lymphoepithelial thymomas--(0.037 +/- 0.004) X 10(9)/L. The data obtained indicate the increased immune depression in the organism in development of tumour process, and depend on degree of its malignization.