The forests of the East Usambara Mountains, Tanzania, are internationally recognized as one of the world's most biodiverse ecosystems. However, despite past conservation efforts they face an ongoing threat from clearing for smallholder agriculture. One potential solution is a „payments for ecosystem services' (PES) program, where farmers are paid to protect forest that lies on their farms. To determine the design of PES program most likely to attract participation, careful documentation of farmer's policy preferences is required. We quantify these preferences and determine willingness to accept values using a choice experiment approach. Notable results are that payment for manure fertilizer (representing an investment in farm productivity) was highly effective at motivating farmer support, a group payment was highly ineffective, and that minimal program conditionality was not always preferred.