Economists have recently grown interested in doing research on research or R & D, as it is called in industrial circles. Several studies have tested Schumpeter's hoary hypothesis that large firms are responsible for most industrial inventive activity.1 Few of these studies, however, suggest why this hypothesis is apparently valid for some industries and not for others. And statistical studies going beyond this question, to try to relate R & D expenditures to firm profit expectations and the availability of funds as in other investment decisions, are rare (Mansfield, 1964; Mueller, 1967). This paper reports the results of an empirical investigation into the determinants of research expenditures in three industries-drugs, chemicals, and petroleum refining. These industries have three advantages for such a study: (1) they are among the leaders in total R & D expenditures; (2) most activity is concentrated in an appreciable number of large or moderately large firms; and (3) government support of research work is relatively small, so that decisions are more closely analogous to ordinary