Abstract: A filter assembly for collecting particulate matter from a stream of sample gas. A filter housing having at least an inlet section and an outlet section supports one or more removable filter elements between adjacent housing sections. At least one end of each housing section is provided with a tapered flange whereby it may be joined to the end of an adjacent housing section. Quick-release clamping means engages the flanges to provide a convenient means for fastening and unfastening the sections of the filter housing without dislodging appreciable quantities of the particulate matter collected on the filter elements. The filter assembly may be expanded as required to accommodate any desired number of filter stages.