The lubrication requirements of a number of gyroscopes have been studied as a prerequisite to the development of improved rotor-bearing lubricants and with the additional objective of replacing proprietary lubricants by one or more lubricants to be specified in the future. The gyroscopes studied included both air-driven and electrically driven types. Measurements were made of bearing temperatures, rotor speed, rate of deceleration, power input, and bearing noise level, the noise components being analyzed. A small high-speed evacuated gyro failed by the time 650 hr of operation had been reached. The other gyros studied all operated without bearing failure for a minimum of 10,000 hr on the specified lubricants. Two electric gyros have operated satisfactorily for 10,000 hr on synthetic diester-type lubricants. Gyro repair facilities reported that the paramount problem in overhaul work is that of obtaining suitable replacement bearings. It has become evident that causes of abnormally short rotor-bearing life include the use of inferior replacement bearings, poor overhaul techniques, and careless handling of equipment. Some of the proprietary lubricants are not suitable for use in instruments which are in storage for long periods.