The California legislature, engine manufacturers, fleet operators, and enforcement agencies have pursued an active program of diesel smoke reduction since 1939. This program has resulted in creditably low smoke levels. While diesels do not contribute substantially to total community air pollution problems, the public complains about the bad appearance of diesel smoke. There are many fruitful approaches for fleet operators to reduce diesel smoke, including more strict maintenance, fuel additive, driver indoctrination, and engine derating. Fleets in the Los Angeles area have achieved excellent smoke reduction by these methods and, at the same time, maintain clean, first-class, economical operations. Two of these fleets are analyzed in this report.