The performance of grease lubricated and unlubricated ball bearings has been examined under various conditions of atmosphere and pressure. Data showing the effect on bearing life by the substitution of “self-lubricating” retainers for standard metallic cages are also included. The tests were run in atmospheres of oxygen, nitrogen, and air, at pressures from 0.5–1 mm Hg absolute to 33 inches Hg, The majority of tests were conducted at 232 C.