The study aimed at morphological evaluation of changes in the lungs of rats during experimentally induced uremia. The studies were performed in three (3) groups of rats: C--a control group (15 animals), SO--15 rats, submitted to sham operation, U--an uremic group--21 rats with experimental renal failure. After 1, 2 and 4 weeks from the surgery, the collected lungs were fixed in Bouin's fluid and in 2.5% purified glutaraldehyde for electron microscopy. Paraffin specimens were cut into 5 microm slices and stained by H+E, by Azan's method and with silver, according to Grimelius. Ultra thin sections contrasted with uranyl acetate and lead citrate. Blood serum urea and creatinine levels were determined. In the uremic rats, increased concentrations of serum creatinine and urea were observed. Chronic renal failure affected the progress and the degree of development of the changes in the lungs, the final effect of which was fibrosis. In microscopic pictures of the lungs from the uremic rats, numerous changes were observed, characteristic for chronic oedematous conditions of different intensification.