Diesel exhaust particulate samples were collected upstream and downstream of an alumina coated metal wool filter mounted in the exhaust system of a 1600 CC Volkswagen engine being operated at idle, 30 MPH and 50 MPH. Dichloromethane extraction of the particulates collected indicates that the filter decreased the amount of soluble organics bound to them. The extracts were subjected to Ames tests. Statistical analysis of the results indicates that on a per ug of extract basis the filter decreased the mutagenic activity of the organics adsorbed to the downstream particles collected at 30 MPH and increased the mutagenic activity of downstream particles collected at idle. Results do not allow a conclusion regarding the effect of the filter on the mutagenic activity of particles collected at 50 MPH. The net effect of the filter on diesel emissions is potentially beneficial.