This SAE Aerospace Recommended Practice (ARP) provides procedures for assuring cleanliness of sampling equipment@ for performing the sampling process@ and for measuring and reporting the sample particle count. The ARP gives procedures for cleaning sample bottles@ when used@ and recommends the solvents to be applied and how these solvents should be prepared. Requirements for the selection of the sampling point@ sampling method@ and sampling frequency are also specified. This ARP also recommends three measuring methods for determining the level of solid particle contamination of hydraulic fluids used in aerospace hydraulics. These are: a. on-line automatic particle counting; b. automatic particle counting method using bottle samples; c. microscopic particle count method using bottle samples.