Limited resources coupled with unlimited demands means that decisions have to be made concerning the allocation of scarce health care resources. The economic instrument of willingness to pay (WTP) is one instrument that can be used to help this decision-making process. Recommendations from the environmental economics literature suggest that the closed end (CE) WTP approach should be used. This approach is just beginning to be used to value health goods. This paper addresses the sensitivity of the closed-ended WTP approach to three issues: the design of the bid vector; the upper and lower limits of integration; and the method of analysis. These are discussed with reference to a study looking at the value of alternative models of ante-natal care in Scotland. The results are discussed and conclusions made concerning the use of the CE WTP instrument for valuing health goods.