A Tapered Element Oscillating Micro-balance (TEOM), consisting of a tapered tube fixed at the wide end with a filter element attached to the narrow end which is free to oscillate, can monitor diesel exhaust particulate by drawing a sample through the filter element. As particulate mass accumulates on the filter, a small change in the frequency of oscillation, directly related to mass, is detected in real-time. As described in this study TEOM sensitivity on the order of 5×10−8 g-sec−1 may be achieved over sample periods of 8-15 seconds. Two light duty diesel vehicles were tested using FTP-Bag III and NYCC driving schedules. For 29 vehicle tests, the mean ratio of total TEOM mass to simultaneously collected 47 mm filter samples was 0.96 (C.V. = 13%). Real-time TEOM data should prove valuable to particulate control technology efforts and environmental impact assessment.