A major limitation to the effectiveness of benefit-cost analyses of proposals involving natural ecosystems is the assertion of existence demand. Not only has confusion arisen regarding its exact definition but little has been done to establish its magnitude. Existence benefits are defined and an empirical study of the value a sample of Canberra residents places on the continued provision of the existence benefits of a particular ecosystem, Nadgee Nature Reserve, is outlined. It is concluded that while the measurement technique employed, the direct questioning of respondents, may be subject to a problem of response bias, it is capable of providing a reasonable estimate of these existence benefits. The average existence value per Canberra adult is at least $20, that is $2 per annum in perpetuity given a 10 per cent real interest rate.