Hybrid-electric transit buses offer potential benefits over conventional transit buses of comparable capacity, including reduced fuel consumption, reduced emissions, and the utilization of smaller engines. Emissions measurements were performed on a 1998 New Flyer 40-foot transit bus equipped with a Cummins ISB 5.9-L diesel engine, an Engelhard DPX catalyzed particulate filter, and an Allison series-drive system. Results were compared to a conventional-drive, diesel powered bus that was equipped with an oxidation catalyst, and to a liquefied natural gas (LNG)-powered bus. Tests were performed according to the guidelines of SAE Recommended Practice J2711. On average, the oxides of nitrogen (NOx) emissions from the hybrid bus were reduced by 50%, compared to the conventional-drive diesel bus, and 10%, compared to the LNG bus. Particulate matter (PM) emissions from the catalyzed filter-equipped hybrid bus were reduced by 90%, relative to those of the conventional diesel bus, and were comparable to those of the LNG bus.