This paper analyzes the effect of intellectual property rights (IPR) regimes on the plant breeding sector in developing countries. Most of these countries have implemented a system of plant variety protection (PVP), or are in the process of doing so, generally as part of their obligations under the Agreement on Trade Related Aspects of Intellectual Property (TRIPS) of the World Trade Organization (WTO). This paper presents the results of research on the initial effects of IPRs on the plant breeding sector in five case study countries (China, Colombia, India, Kenya and Uganda). Three of the countries have PVP systems in place and the other two are in the process of either developing or implementing legislation. But the ease of implementing PVP seems to have been overestimated. Opportunities to minimize the transaction costs of acquiring and enforcing rights are being missed. Detailed interviews with both domestic and international seed companies suggest that PVP can not be expected to initiate the development of a commercial seed sector. But a well functioning system can play a role in stimulating further development of the sector, although a measured approach to increasing the scope of protection will probably better balance interests than rapid adoption standards of industrialized countries. The results also highlight the particular challenges facing national agricultural research institutes in determining how to best make use of IPRs, such as PVP, particularly given broader changes in publicly-financed agricultural research.