This is the latest in a series of papers on the subject of the costs and benefits of diesel particulate control. The initial focus was on new light duty vehicles with a gradual shift to heavy trucks and buses. This latest study considers in-use urban buses and explores the relative costs and benefits of three alternative control strategies - retrofit of trap oxidizers, introduction of inspection and maintenance and conversion to methanol fuel. It concludes that retrofit is very cost beneficial and could be made more so by the addition of I/M. Conversion to methanol results in the maximum particulate reduction but is not as cost beneficial for the particulate reduced as is retrofit.