Identification of vehicles whose plates indicate they are wanted (e.g., stolen or involved in the commission of felonies) or whose drivers may be operating illegally is based on the use of rapid, computer-based mass screening of vehicle registration plates of either parked vehicles or those in motion. The legality of such screening was affirmed by the Office of the Maryland Attorney General. The demonstration project was carried out in Baltimore County from 1973-1977. For the screening, a list was prepared of vehicle license tags warranting attention by law enforcement officers and stored in a small computer system in an observation vehicle. An observer types the plate numbers of passing vehicles. If there is a match, the tag number and the reason it is on the list is displayed, giving reasonable cause, in many cases, for further police action. Two separate phases of the mass screening project were implemented. The first used a separate vehicle for observations; the second placed the screening function in State patrol cars. A comparison of the results of the mass screening and those of normal police operations in Baltimore County during the first quarter of 1977 showed that the mass screening produced an appreciably higher yield of citations for driving while licenses were suspended, revoked, canceled, or refused than the normal operations. However, further research is needed to determine the advisability of mass screening. Photographs, tables, footnotes and a bibliography of 12 references are included. Six appendixes describe the operations of the project in detail.