The exocrine pancreases of 25 male inbred rats of a Wistar strain were investigated by electron zymogen granules: enzyme proteins: pancreas; ultrastructure; rat microscopy and histochemistry 1, 2, 3, 5 and 7 days after 5/6-nephrectomy, which was performed in order to produce a uremia. Sham-operated and normal animals were used as controls. Under the influence of the acute uremia, a complex impairment of the pancreatic acinar cell appeared with destruction, in the form of focal cytoplasmatic degradation and the formation of cytolysosomes, and with a temporary disturbance of the rough endoplasmic reticulum, which led, until the end of the second day of the experiment, to an extensive stoppage, and latter to a reduction, in the synthesis of exportable enzymes. The function of the Golgi-apparatus and thereby the formation of zymogen granules is discontinued until at least the end of the third day of the experiment. Afterwards the production of zymogen granules is disturbed qualitatively and quantitatively. Here a deficiency in energy with mitochondria damage and a subsequent disturbance of intracellular transport in connection with an inhibition in membrane formation might be taken into consideration as pathogenetical factors. The following are discussed as possible causes of the metabolic-toxic damage of the acinar cell during uremia: lowmolecular toxic proteins, depletion of amino acids, intracellular pH-displacement and a deficit of phosphates rich in energy.