This SAE Aerospace Information Report (AIR) presents data on normally accepted changes in physical properties and contamination levels for MIL-PRF-5606, MIL-PRF-83282, and MIL-PRF-87257 hydraulic fluids used in hydraulic test stands. This information is of importance to all users of hydraulic test stands to assure the performance data obtained on these test stands for specific components will not be adversely affected by excessive changes in fluid properties or contamination levels.