Particulates are removed from a particulate-laden gas stream such as the exhaust gas from an internal combustion engine by passing the gas through a cyclone type inertial separator. The separator has particulate reject slots cut in the side wall of the cyclone chamber through which particulates are rejected into a collection chamber. The collection chamber can be filled with a porous material such as wire mesh or expanded metal. The bottom of the cyclone chamber is a nonperforate plate. The separator can be built into a muffler. Performance is improved by including an agglomeration unit between the engine and the separator. The agglomeration unit comprises a housing inserted in the exhaust gas stream between the engine and the separator which contains a pervious mass of metal bodies such as wire mesh or expanded metal lath, or alternatively contains an alumina. Performance can be still further improved by placing a filter unit downstream from the separator.