A hybrid tandem mass spectrometer is constructed by interfacing a quadrupole mass filter (Q) to a quadrupole ion trap mass spectrometer (QITMS) and is evaluated for the analysis of mixtures. The mass filter is set to selectively inject ions of a particular m/z or, in scanning mode, to sequentially inject ions into the QITMS for subsequent manipulation and detection. Performance of the instrument is demonstrated using a mixture of ions created by electron impact ionization of perfluorotributylamine (FC-43) and peptide ions generated by pulsed Cs+ bombardment. Resulting data are compared to those obtained by utilizing only the ion trap. Molecular weight, fragmentation, and high-resolution analyses for the sequentially injected mass-filtered peptides show improved performance over similar measurements employing only the ion trap mass spectrometer. Performance is optimized when ions are not rf-isolated in the QITMS. Using the hybrid, a resolution of 33,200 is achieved for angiotensin I. Dramatic reduction of space charge-induced signal suppression is demonstrated for LSIMS of Glu-fibrinopeptide B. 'On-the-fly' collision-induced dissociation is performed for m/z 502 from FC-43, where fragmentation is induced by increasing the ion injection energy. Collision-induced dissociation efficiencies for fragmentation of angiotensin I by resonance excitation are investigated as a function of cooling time for different modes of operation of the hybrid. A current limitation of the instrument is the time required to port the data for acquisition.