AbstractThe purpose of this study was to determine the economic costs of school‐based mouthrinsing in the demonstration programs. Costs for two complete years were expressed in 1978 dollars, and divided into explicit and implicit categories. Costs per participant were found to vary among programs (ranges of average total costs ‐ period I: $2.35‐$8.05, period II: $1.46‐$7.94), and a tendency for some average costs to increase with size was identified. That costs were higher than the conventionally reported $0.50‐$1.00 reflects 1) the organization of these federally funded programs and, 2) the use of an accounting method which describes the real economic costs of public