During the 1950s and 1960s, quantitative research on the economics of invention was spurred by awareness that technical change was a primary source of the rapid economic growth achieved by industrialized nations. A leader in this effort was Jacob Schmookler, whose analysis of patent statistics [2] [4] provided the first demonstration that. inventive activity is responsive to the pull of demand. The motivation now is different but no less compelling: a decade of retarded productivity growth makes it imperative to understand the forces governing the rate of technical advance. This paper retests Schmookler's demand-pull hypothesis with a new and more comprehensive data set.