In this paper the concept of knowledge circulation is explored and placed in a social systems approach that distinguishes four types of "capital": cultural, strategic, network and economic. Knowledge circulation is a form of university-industry interaction that accommodates the objectives of what are, in many respects, unequal partners and outlines the capital gains for all participants. In the final section, the implications for the internal and external marketing of science are presented. (Contains 2 tables and 2 figures.)