A reproducible method for the preparation of 75S ribosomes from cysts of Entamoeba invadens is presented. The method depends on the inactivation of the cyst's ribonuclease by high levels of Bentonite. The ribosomes are found to be extremely sensitive to ribonuclease, and to be stabilized by the addition of manganous and calcium ions to the magnesium customarily employed. Reasons are given for equating these ribosomes with the particles of which the crystalline chromatoid bodies are made.