The paper analyses ex ante the economic implications of transgenic virus- and weevil-resistant sweet potatoes in Kenya. These technologies are being developed within international projects, involving public and private organisations. It is expected that the resistant varieties will significantly reduce the crop losses in farmers' fields. Model calculations show that both innovations are likely to bting about substantial growth in economic surplus. The projected annual gross benefit is 5.4 mUS$ (million US$) for virus resistance and 9.9 mUS$ for weevil resistance. Due to the semi-subsistence nature of sweet potato, the producing households will be the main beneficiaries. However, market consumers will also capture about one-fourth of the aggregate welfare gains. The high profitability of the projects is confirmed by significantly positive returns on research investments. The examples demonstrate the viability of successful research partnerships between the public and private sectors. As most of the basic biotechnology tools available to date are patented by private companies in the North, which often do not have sufficient market incentives to develop end-technologies for the South, more interactions of this kind are required from a development policy perspective. Working with typical semi-subsistence crops is particularly appealing because it immediately targets the poor and avoids conflicts with the private sector's commercial interests.© 2001 Elsevier Science B.V. All rights reserved.