The mission of the Pharmacology Core is to provide analytical and pharmacokinetic support for Research Projects in this application. Pharmacology Core staff will provide advice on design of pharmacokinetic studies and sampling protocols, coordinate the collection and proper storage of all blood samples for the Program, perform measurements of serum or plasma concentrations of drugs and metabolites, and provide pharmacokinetic analyses for the laboratory projects. By establishing a central facility for planning and coordination of blood sampling protocols and the analysis of drug and/or metabolite concentrations in blood and other biological samples, this Core will minimize duplication f efforts and maximize success in obtaining the analytical and pharmacokinetic precision and information needed to accomplish the proposed research. High performance liquid chromatographic and gas chromatographic-mass spectrometric assays are available to measure plasma concentrations of drugs and metabolites for Projects 11 and 8. Core staff have developed assays for busulfan and for pentoxifylline and its active metabolites (M1 and M5), for the proposed research projects. Additionally, this Core will assist Project 8 with separation and purification of PTX analog enantiomers and will include a research component addressing several aspects of BU pharmacokinetics as they relate to improving methods of BU administration in transplant patients. As a centralized facility, the Pharmacology Core will assure dependable, high quality analytical support for the pharmacokinetic aspects of the supported research projects in an economical manner.