Packed fused-silica columns of 0.25-mm I.D. have been interfaced to a quadrupole mass spectrometer by direct coupling and to a magnetic mass spectrometer with a moving-belt interface. Electron impact (EI) and chemical ionization (CI) spectra were obtained by both techniques. Using the direct-coupling interface, we have successfully analyzed and obtained molecular ions for a number of compounds that are too thermally labile for analysis by gas chromatography-mass spectrometry. However, extremely thermally labile compounds, such as sulfonylureas, did not give MH+ ions in their CI spectra due to thermal degradation in the capillary interface line. With the moving-belt interface, MH+ ions were obtained for sulfonylureas in the CI mode. Better quality chromatograms and spectra, and better EI sensitivity were obtained with the moving-belt interface than by direct coupling.