The objective of this study is to analyze the determinants of private agricultural R&D investment in the United States and the liaison between public and private R&D sectors. The empirical analysis employs U.S. agricultural data for the 1970-1996 period. The results show that federal R&D obligations for basic research, used as a proxy for the complementary role of public R&D, have a significant and positive impact on private agricultural R&D spending. In contrast, federal R&D obligations for applied research, used as a proxy for the substitute role of public R&D, are not found to have a significant impact.