In 27 patients with uncontrolled type 1 diabetes the changes of the endogenous TNF alpha serum concentration in correlation with blood glucose level were investigated. In the first 24 hours period, the concentration of glucose was analysed in the following way: immediately after the admission, next every hour for three hours and then after 6, 9, 12, 18 and 24 hours. In the followed days the blood glucose was determined five times a day. The serum concentration of endogenous TNF alpha was monitored immediately after the admission, after first hour of treatment and next after 6, 24, 72 hours. The control group consisted of 23 healthy persons. Glycaemia level and TNF alpha concentration were analyzed with Student-1 test for combined variables and the correlation Spearmann test. The level of TNF alpha markedly decreases together with the decrease of blood glucose level in each patient. The level of TNF correlates with the level of glycaemia (linear correlation). The results presented above unequivocally show that there is a correlation between endogenous TNF alpha and glucose level in serum of the patients with type 1 diabetes (at the decompensation stage of the disease).