Twice each year, the Cement and Concrete Reference Laboratory (CCRL), housed at the National Institute of Standards and Technology (NIST), issues two proficiency samples of portland cement to be evaluated by hundreds of testing laboratories throughout the United States using ASTM standard test methods . The chemical characteristics and performance properties of these cements are therefore extremely well documented , making them ideal systems to study with the NIST cement hydration and microstructural development computer model (CEMHYD3D) [3,4]. In this report, scanning electron microscopy (SEM) images and quantitative phase analysis results for cements 135 and 136, issued in January of 2000, will be presented and compared to the potential phase composition determined via ASTM C150 . Additionally, CEMHYD3D and supplemental experimental measurements will be applied to predicting the hydration kinetics, heat of hydration, and mortar strength development of the two cements. The latter two properties can be compared to those measured as part of the CCRL proficiency sample analysis program.