Lungs are the target organ in chronic hyperglycemia, but its large reserves causes a subclinical course of these changes. Given the results of other researchers indicating reduced active surface of gas exchange and pulmonary capillary damage, it can be assumed that diabetes and other hyperglycemic states diminish these reserves and impair effectiveness of respiratory gas exchange during pneumonia. So it is plausible to observe coexistence of glucose metabolism disorders and respiratory failure in patients hospitalized with lower respiratory tract infection. An observational study was conducted on 130 patients hospitalized with bacteriologically confirmed pneumonia. 63 patients suffering from chronic glucose metabolism disorders (A) and 67 randomly selected patients in control group (B) were observed on laboratory and clinical findings. There was no significant difference in prevalence of acute respiratory failure, although in the study group a slightly greater number of patients diagnosed with acute respiratory failure was observed. There was a significantly greater number of patients with previously confirmed chronic respiratory failure using long-term oxygen theraphy in A group (p = 0.029). The B patients with average blood glucose level > 108 mg/dl had significantly lower partial pressure of oxygen (PaO2)(gIc ≤ 108: 58.6 +/- 9.8; glc > 108: 51.7 +/- 11.1; p = 0.042). There was a statistically significant negative correlation of the average blood glucose level and PaO2 in the control group (p = 0.0152) and a significant inverse association between the average blood glucose level and the partial pressure of oxygen in patients without COPD belonging to the control group (p = 0.049). Respiratory failure is frequent in patients hospitalized with pneumonia. In patients without chronic glucose metabolism disorders with blood glucose level rising the oxygen tension decreases The association is stronger in patients without COPD.