Marketing several environmental services from a single area can help access diverse sources of funding and make conservation a more competitive land use. In Bolivia's Los Negros valley (Department of Santa Cruz), bordering the Amboró National Park, 46 farmers are currently paid to protect 2774 ha of a watershed containing the threatened cloud-forest habitat of 11 species of migratory birds. In this payment for environmental services (PES) scheme, annual contracts prohibit tree cutting, hunting and forest clearing on enrolled lands. Farmer-landowners as service providers submit to independent yearly monitoring, and are sanctioned for non-compliance. Facilitated by a local NGO, Fundación Natura Bolivia, one service buyer is an international conservation donor (the US Fish and Wildlife Service) interested in biodiversity conservation. The second service users are downstream irrigators who likely benefit from stabilized dry-season water flows if upstream cloud forests are successfully protected. Individual irrigators have been reluctant to pay, but the Los Negros municipal government has on their behalf contributed ~ US$4500 to the scheme. The negotiated payment mode is annual quid pro quo in-kind compensations in return for forest protection. Predominantly, payments are made as "contingent project implementation", transferring beehives supplemented by apicultural training. With regard to service provision, environment committees and education programs have increased awareness in downstream communities of the probable water-supply reduction effect of continued upstream deforestation. External donors have funded subsequent studies providing basic economic, hydrological and biodiversity data, and covered PES start-up (~ US$40,000) and running transaction costs (~ US$3000 per year over the last three years). The greatest challenges in the development of the PES mechanism have been the slow process of building trust between service buyers and providers, and in achieving clear service-provision additionality. © 2007 Elsevier B.V. All rights reserved.