The use of a corona-less electrostatic precipitator as a collection and agglomeration device for diesel soot has been investigated. It collects and grows diesel particles which are emitted in the submicron diameter range and grow into much larger particles. These larger particles may then be collected with a relatively simple inertial device.Previous testing of a full scale precipitator designed for a Caterpillar 3304 engine showed that the reduction in sub-micron sized mass from the engine was roughly 30 to 40%. Greater reductions were desired. A sub-scale electrostatic agglomerator was built to analyze in greater detail the behavior of an existing full scale device. Tests were designed to determine; the charged fraction of the particles from the engine used, the collection efficiency of the electrostatic agglomerator, the effect of geometry on collection efficiency, and the size distribution of the particles reentrained after electrostatic collection.The results of that testing showed that; roughly 80% of the soot from the engine carried a charge, the overall collection efficiency of the precipitator/agglomerator was about 40%, the best collector proved to be a square tube geometry, and the mass mean diameter of reentrained particles was greater than 20 μm.