It is proposed to develop the analytical potential of gas chromatography-mass spectrometry for 1) profiling the urinary excretion of modified nucleosides in patients with various neoplasms; 2) determination of the excretion levels of 2'-O-methylated nucleosides of normal patients and patients with cancer of various types; and 3) studying the metabolism and to quantitate the distribution and excretion of psi ox, the periodate oxidation product of pseudouridine, in the urine and tissues of mice. As a corollary to the above objectives, methods will be developed for the incorporation of stable isotopes into nucleic acid bases, nucleosides, and nucleotides of biochemical and medicinal interest. These labeled compounds will then be used as internal standards to explore the utility of gas chromatography-mass spectrometry for the determination of the in vivo concetration, metabolism, distribution, and excretion of nucleic acid analogs. Synthetic procedures to be utilized include various oxidation, reduction and exchange reactions for the incorporation of deuterium, oxygen-18, and nitrogen-15 into the aglycone and carbohydrate portion of nucleosides and nucleotides. Gas chromatographic-mass spectrometric procedures to be investigated include chemical ionization, single- and multiple-ion monitoring, and metastable defocusing. Application of these techniques to the determination of the concentration, metabolism, and excretion of nucleic acid analogs in blood, urine, and tissues of experimental animals will then be studied.