Particulate and manganese mass emissions have been measured as a function of mileage for four Escort and four Explorer vehicles using 1) MMT (Methylcyclopentadienyl Manganese Tricarbonyl) added to the gasoline at 1/32 g Mn/gal and 2) gasoline without MMT. The MMT was used in half of the fleet starting at 5,000 miles. The vehicles were driven on public roads at an average speed of 54 mph to accumulate mileage. This report describes the particulate and manganese emissions, plus emissions of four air toxics at 5,000, 20,000, 55,000, 85,000 and 105,000 miles. Four non-regulated emissions were measured and their average values for vehicles without MMT were 0.6 mg/mi for formaldehyde, 0.7 mg/mi for 1,3-butadiene, 9 mg/mi for benzene and 12 mg/mi for toluene. Corresponding values for MMT-fueled vehicles were between 1.5 and 2.4 times higher. Of the total manganese used in the fuel, between 5% and 45% was emitted as airborne particulate matter, 8% was found in the oil, and the remainder was probably stored in the engine, catalyst and the exhaust system. The manganese that was emitted was in the 100 to 450 μg/mi range and increased with mileage accumulation. The EPA reports that manganese emissions of this magnitude may represent a health hazard. The total particulate emissions were between 0 and 5 mg/mi, increasing with mileage accumulation and with MMT usage.MEASUREMENTS OF REGULATED and so-called “non-regulated” emissions are required to show that gasoline additives do not cause emissions that could harm the environment. In general, a fuel additive could cause such damage either directly by forming harmful combustion products or indirectly by damaging vehicle emission control systems.Methylcyclopentadienyl manganese tricarbonyl (MMT) is an anti-knock gasoline additive whose combustion products accumulate in engines *, deposit on exhaust catalysts [2, 3], and are emitted into the atmosphere [4, 5]. In each case, they have the potential to harm the environment. In engines, they increase the regulated emissions , especially of hydrocarbons. More recent work [6, 7] on low levels of MMT (1/32 g/gal) in gasoline confirms the increased emission of hydrocarbons. On catalysts, combustion products of MMT cause deactivation [2, 3], and as air-borne particulate matter, they can cause neurological effects similar to Parkinson's disease .The magnitudes of these effects depend on the level of MMT added to the gasoline and, perhaps, on the vehicles. In this work, the exhaust emissions from four vehicles, two 1.9L Escorts and two 4.0L V6 Explorers, using MMT fuel at 1/32 g Mn/gal are compared to those from four identical vehicles using MMT-free fuel. These vehicles were equipped with sequential electronic fuel injection and three-way catalyst emission control systems. This report describes the particulate and manganese emissions, as well as emissions of four air toxics, from tests at 5, 20, 55, 85, and 105 thousand miles and summarizes the effects of mileage accumulation. An earlier report  discussed interim results to 55,000 miles.