This paper describes the results of tests for diesel smoke reduction by gasoline fumigation using an ultrasonic atomizer, developed by TONEN Corporation. The spray of this ultrasonic atomizer is characterized by fine droplets of uniform size and low penetration. This means that the spray can be easily influenced by ambient air and delivered effectively to the cylinders. Based on these characteristics we proposed to reduce diesel smoke by fumigation, injection of fuel into the intake manifold.Gasoline was chosen as the fumigation fuel due to its ease of evaporation and easy handling. The fumigation tests were conducted on an engine running at full load producing dense smoke emissions. A commercial four cylinder diesel engine fitted with an ultrasonic atomizer to its intake manifold produced 50% smoke reduction at 15% fumigation ratio and approximately 70% smoke reduction at 30% fumigation ratio. However, other emissions, especially HC and CO, increased significantly.