1. Native or partially degraded RNA derived from intact rat liver, or from the parenchymal-cell or the non-parenchymatous fraction of liver, has been shown to be transported into rat parenchymal cells in suspension, without prior degradation to acid-soluble components, when the cell suspension is incubated with the RNA at 37 degrees . The amount of RNA of exogenous origin present in the parenchymal cells in an acid-precipitable form increased rapidly up to 30-60min., after which it gradually decreased, indicating intracellular degradation to acid-soluble components of the RNA taken up by the cells. 2. The RNA taken up by the parenchymal cells from the medium, and the acid-soluble products of its degradation within the cells, could be released back into the medium. 3. The RNA of exogenous origin present in acid-precipitable form in the parenchymal cells represented up to 5% of the RNA of the cells after 60min. of incubation. 4. When the concentration of RNA in the medium was less than 200mug./ml., over 10% of the RNA was transported in an acid-precipitable form in 60min. into the parenchymal cells incubated at a concentration of 2.3x10(6)/ml. 5. Ribonuclease inhibited the uptake of exogenous RNA by the parenchymal cells, whereas 2,4-dinitrophenol, sodium azide, protamine sulphate and polyvinyl sulphate had no significant effect. 6. The uptake of exogenous RNA by liver slices proceeded at a rate which was 4-20% of that obtained in the parenchymal-cell suspensions; the RNA taken up did not appear to become degraded, unlike that taken up by the cell suspensions. 7. It is concluded that dispersion of liver tissue to a suspension of single cells increases the permeability of the parenchymal cells to macromolecular RNA and creates conditions that lead to a rapid degradation of the RNA taken up.