The subchronic intravenous application of microcrystalline cellulose (MCC), in a dose of 5 mg/kg twice weekly for 10 weeks, resulted in servere crystal embolism in the lungs of the animals. The clinical parameters were either unchanged (erythrocyte and leucocyte counts, differential blood picture, osmotic resistance of the erythrocytes, total serum bilirubin, serum protein and serum protein fractions) or slightly pathological (hemoglobin content, hematocrit, GOT and GPT). The results from tests of the liver function (by means of bromosulphthaleine clearance) and of the renal function as well as the ophthalmologic examination were not indicative of damaged parenchyma or disturbed microcirculation. Intra-arterial infusions of MCC affected the peripheral muscular blood supply, blood pressure and heart rate.