This chapter discusses the isolation of RNA from yeast, where yeast RNA (ribonucleic acid) is obtained by extracting a whole cell homogenate with phenol. The concentrated solution of phenol disrupts hydrogen bonding in the macromolecules, causing denaturation of the protein. The turbid suspension is centrifuged and two phases appear, the lower phenol phase contains DNA (deoxyribonucleic acid) and the upper aqueous phase contains carbohydrate and RNA. Denatured protein, which is present in both phases, is removed by centrifugation. The RNA is then precipitated with alcohol. The product obtained is free of DNA but usually contaminated with polysaccharide. Purification can be made by treating the preparation with amylase. Suspend thirty grams of dried yeast in one hundred and twenty millilitre of water previously heated to thirty seven degree centigrade. Cool the solution in ice and leave to stand for one hour. Wash the RNA with ethanol-water, ethanol, and finally ether, air dry and weigh.