This paper explained the use of a contingent valuation technique, which the author labelled 'participatory environmental valuation', to assign monetary values to non-traded forest products. Individual respondents were asked to rank forest products in order of importance and then to use counters to score both the products and a comparative numeraire (yardstick) of their choice, which could be any traded commodity of local significance. Local residents were found to place a particularly high value on water and grazing resources in Oldonyo Orok forest in Kenya. Altogether, annual benefits of forest use were estimated at almost KSh 5000 per household, which provided a convincing justification for conservation.