The assessment of gene function, which follows the completion of human genome sequencing, may be performed using the tools of the genome program. These tools represent high-throughput methods evaluating changes in the expression of many or all genes of an organism at the same time in order to investigate genetic pathways for normal development and disease. They describe proteins on a proteome-wide scale, thereby, creating a new way of doing cell research which results in the determination of three dimensional protein structures and the description of protein networks. These descriptions may then be used for the design of new hypotheses and experiments in the traditional physiological, biochemical, and pharmacological sense. The evaluation of genetically manipulated animals or new designed biomolecules will require a thorough understanding of physiology, biochemistry, and pharmacology and the experimental approaches will involve many new technologies including in vivo imaging with SPECT and positron emission tomography (PET). Nuclear medicine procedures may be applied for the determination of gene function and regulation using established and new tracers or using in vivo reporter genes such as genes encoding enzymes, receptors, antigens, or transporters. Pharmacogenomics will identify new surrogate markers for therapy monitoring which may represent potential new tracers for imaging. Also drug distribution studies for new therapeutic biomolecules are needed at least during preclinical stages of drug development. Finally, new biomolecules will be developed by bioengineering methods, which may be used for isotope-based diagnosis and treatment of disease.