A coupled liquid chromatography/tandem mass spectrometry assay was developed for simultaneous determination of Ro 48-6791 and its secondary amine metabolite in human plasma samples with a quantification limit for both compounds of 1 pg/mL using a 1 mL plasma aliquot. The method exploits the enhanced mass sensitivity of a microbore (300 microns i.d.) reversed-phase capillary column coupled to an ion spray probe combined with tandem mass spectrometry. A straightforward column-switching system was utilized to focus the analytes onto a microbore trapping column following solid-phase extraction of a 50 microL plasma sample extract from liquid/liquid extraction. Backflushing of the retained analytes from the trapping column onto the microbore capillary column provided the requisite high peak concentration for high sensitivity. The inter-assay precision and accuracy for Ro 48-6791 and its metabolite, at 10 pg/mL, were found to be 3.4%, and 105%, and 9.1%, and 99.9%, respectively. The calibration curves were linear over the range 1 to 1000 pg/mL. The method proved to be sufficiently rugged for analysis of samples.