Several current methods for the extraction and estimation of nucleic acids in biological materials were applied toEuglenaand other plants. The efficiency of both the preliminary extractions for acid-soluble-P and lipid-P and the subsequent extraction of the nucleic acids was studied. A relatively high acid concentration (15% TCA) was required to directly extract all the acid-soluble phosphates. These conditions appeared to remove a small amount of the RNA. Lower acid concentrations as used in the Ogur–Rosen method (2% PCA) failed to extract all the acid-soluble phosphates. By using a modification of the Ogur–Rosen initial extraction method, the acid-soluble phosphates were quantitatively extracted without loss of RNA. After removal of the acid-soluble phosphates and lipid phosphates, the plant nucleic acids were quantitatively extracted by either the Schmidt–Thannhauser or Schneider methods. In many of the plants tested, the presence of pentose-containing polysaccharides, protein degradation products, or polyphosphate (algae only) interfered in estimations based on either the Schneider or Schmidt–Thannhauser procedures. Such interfering substances in the Schmidt–Thannhauser method were eliminated by the use of an anion exchange resin. Details are given of a modified Schmidt–Thannhauser procedure which should be suitable for a wide range of plants. The modified procedure may be simplified forEuglenaand some higher plant tissues depending on the nature and quantities of interfering substances present. Methods are also given for the quantitative separation of plant RNA nucleotides by paper chromatography and by ion exchange paper chromatography.