The light-duty diesel vehicle has been targeted for some years as a contributor to the visibility problem in many urban areas.The Colorado Department of Health. Air Pollution Control Division, has conducted a pilot inspection/maintenance program for the purpose of evaluating the effectiveness of a loaded mode inspection program in reducing diesel opacity and particulate emissions levels.The study consisted of screening approximately 200 vehicles using a loaded mode test cycle and exhaust opacity measurements to select a test population of 13 vehicles. Those vehicles exceeding a given opacity standard were subjected to the Federal Test Procedure (FTP) both before and after repairs. The vehicles subsequently underwent a series of maintenance sequences. The repair effectiveness of each sequence, as well as overall repair effectiveness, for opacity, gaseous and particulate emissions reductions was quantified and is presented in this report along with the associated retail costs of repairs.