The papers collected in this volume were presented at the 5th International Symposium on Mass Spectrometry in Biochemistry and Medicine held at Rimini, Italy, in June 1978. This meeting was organized by the Italian Group for Mass Spectrometry in Biochemistry and Medicine, which was founded in Milan, Italy, in 1975 by researchers working in different fields (chemistry, pharmacology, medicine, biology). I wish to thank Mrs. Anna Bernard, Mrs. Donata Castoldi and Miss Vanna Pistotti for their invaluable technical assistance and countless eff. orts in the preparation of this volume. Alberto Frigerio Milan, March, 1979 v Contents The Place of Mass Spectrometry in Drug Metabolism Studies ...1 A. Benakis In Vitro and in vivo Studies on the Metabolism of Dibenzo/c,f 7-/-1,2 7 Diazepine ********. ********* 9 A. Frigerio, P~ Negrini, D~ Rotilio, A. De Pascale and E. Rossi Gas Chromatographic-Mass Spectrometric Identification of Urinary Metabolites of Propildazine in Rat 27 L. Simonotti, R. Colombo and G. Pifferi Mass Spectrometric Characterization of Sydnocarb ~ and its Major Metabolites in Rat ***************** 43 J. Tamas, M. Polgar, G. Czira and L. Vereczkey Metabolism of an Aryloxy Beta Blocking Drug 53 G. L. Passetti, E. Grassi and A. Trebbi Isolation and Identification of the Chloroform Soluble Urinary Metabolites of Suloctidil in Man . ****. . ** 69 R. Roncucci, W. Cautreels, M. Martens, C. Gillet, K. Debast and G. Lambelin Are Stable Sulfenic Acids Possible Metabolites of Suloctidil? ...85 W. Cautreels, M. Martens, R. Roncucci, C. Gillet, K. Debast and G.