Governments now expect universities to behave entrepreneurially generating revenues from the commercial exploitation of their intellectual assets ("third stream" income). This study questions whether this is possible for all universities in the UK and for all disciplines, or whether there are differences between institutions, between disciplines and even between disciplines in a single institution. Using research income from industry, charity and government departments for the period 1996-2000 as a proxy measure for third stream income, the performance of 16 UK institutions in four different disciplines (physics, engineering, history and education) was compared. Income from third stream sources varied significantly by institution and by discipline. There was also a significant disciplines x institution interaction, so that potential for generating third stream income cannot be predicted from either discipline or institution alone. A number of explanatory factors for this are considered, and the implications for university decision-making, strategy development and collegiality are discussed. (Contains 3 tables and 1 figure.)