Radiolytic damage to the ditolylmethane organic coolant-moderator of the ARBUS reactor was removed by vacuum distillation. The majority of the ditolylmethane degraded formed gaseous and high-boiling materials, which were easily removed by the vacuum distillation. Unsaturated hydrocarbons and low-boiling residues were a minor contribution to the impurities produced by radiolysis in the primary coolant loop. Radioactivity in the primary coolant loop was found to be caused primarily from corrosion products of the system, 16N from dissolved oxygen, and impurities in the coolant-moderator. These also were significantly reduced in the vacuum distillation process.