This study was aimed at defining resilient properties (resilient modulus, Poisson's ratio) of asphalt treated base (ATB) under repeated loading. A brief program of testing these materials, as found in the Washington State University test track and several in service pavements in western Washington, was included. The purpose of these tests was to assist in defining the properties of field constructed ATB materials. A very sophisticated dynamic triaxial testing system was designed, constructed, and utilized. Testing parameters for a wide range of conditions were determined and analyzed. The resilient modulus was correlated with conventional tests and this approach shows promise for the transition from empirical to more basic engineering tests.