The travel-cost method of estimating a recreation demand function requires specifying the functional form of the first-stage demand curve and defining the width of the concentric origin zones. A Monte Carlo approach is used to determine the sensitivity of demand and valuation estimates to alternative choices about these two issues. Demand and valuation estimates are shown to be sensitive to the definition of the orgin zone and to the use of a semilog versus a double log first-stage demand curve. The proper choice or origin zones is unclear, but a semilog form is more appropriate than a double log form.