Bulldozer noise is the most serious noise problem for surface miners today. Not only are bulldozers the most common type of mobile equipment, but the majority of their operators are also exposed to more noise than current federal regulations allow. In 1977, the Bureau of Mines responded to this problem by developing retrofit noise control treatments which reduce the noise that reaches the operator. These treatments were specifically designed to be readily installed in the field at low cost. In 1978, these treatments were installed on two Caterpillar D9G’s in surface coal mines to demonstrate the noise reduction that can be achieved under actual production conditions. This paper presents the results of the field demonstrations.