The purpose of this study was to investigate various aspects of the modeling methodology appropriate to the measurement of opiate receptors in vivo with 18F-cyclofoxy and position emission tomography. These studies include: 1) the measurement of the component of non-specific binding with paired studies using the active (-) and inactive (+) enantiomers of cyclofoxy, 2) development of an appropriate infusion protocol for producing true equilibrium aimed to optimize human studies, 3) the use of varying specific activities of tracer to perform absolute quantitation of receptor concentration, and 4) the study of the kinetics of displacement. On the above four projects, four studies have been performed in project 1, 3 in project 2, and 1 in project 4. Preliminary analysis of these data have shown that there is uniform non-specific binding in the brain and that no region may serve as an accurate "null" region with the active enantiomer. In addition, a simple infusion scheme has been developed and will be applied to the human studies in the near term.