Our principal objective is to develop and apply new, improved methods for analysis of biological materials that require mass spectrometric (MS) analysis, but which have not previously been amenable to such analysis by reason of volatility, thermal lability or charge state. Our basic approach involves a direct interface of high performance liquid chromatography (HPLC or LC) effluent with the mass spectrometer source, and permits use of conventional solvent flow rates and buffered aqueous solvents (l ml/min o.l M ammonium acetate). Ions are desorbed directly from vapor droplets that are heated rapidly in passage from the HPLC capillary through the ion source by a mechanism that resembles other desorption techniques (field desorption, laser desorption, fast atom bombardment (FAB)). Thermospray LC/MS has the important advantages over these other methods of a) a chromatographic inlet, b) applicability to analysis of mixtures, and c) simplicity of sample preparation. Recent applications include: 1) Identification and quantification of novel fatty acid conjugates of carnitine in subjects with Reye's Syndrome, organic acidurias and valproic acid toxicity; 2) Separation and quantification of cortisol in human plasma. Development of stable isotopic tracer methods using d3-cortisol prior to use in studies of cortisol production rates in children. Tracer levels are readily measured at 1-4% of total plasma cortisol. 3) Separation and quantification of glucose in human plasma prior to use of uniformly labelled C13 labelled glucose (98 atom % excess) as tracer for production and turnover rate studies in type I glycogen storage disease. 4) Identification of a variety of glucuronide and glutahione conjugates that were intractable to mass spectrometric analysis by other methods.