Fifteen reports from 10 studies that measured diesel exhaust inside 56 school buses: 34 conventional buses; 13 retrofit buses; three clean technology buses; one conventional bus with and without retrofit; four CNG buses; and, one bus with both diesel and CNG were identified. The reports each included measurements of at least one of six markers of diesel exhaust particulate. Three studies also used a marker to quantify diesel exhaust in bus cabins, two used a tracer gas (SF6) injected into the bus exhaust system, while the third used an organic iridium compound that was added to the diesel fuel. The SF6 studies did not adequately control for potential confounding, exposure estimates ignored the performance characteristics of the buses being tested, and some conclusions were based on selected sub-sets of data. The iridium study tested only a single bus and did not consider whether addition of that metal to diesel fuel reduced diesel particulate emissions. Both tracer methods failed to consider crankcase emissions and it is not clear that either method can directly address this concern without the use of a crankcase tracer. This is an abstract of a paper presented at the AWMA's 99th Annual Conference and Exhibition (New Orleans, LA 6/20-23/2006).