This study uses a sample of Japanese university scientists in life and materials sciences to examine how academic entrepreneurship has affected the norms and behaviors of academic scientists regarding sharing scientific resources. Results indicate that high levels of academic entrepreneurship in a scientific field are associated with less reliance on the gift-giving form of sharing (i.e., generalized exchange) traditionally recommended by scientific communities, and with a greater emphasis on direct benefits for givers (i.e., direct exchange), as well as a lower overall frequency of sharing. We observe these shifts in sharing behavior even among individual scientists who are not themselves entrepreneurially active; this suggests a general shift in scientific norms contingent on institutional contexts. These findings reflect contradictions inherent in current science policies that simultaneously encourage open science as well as commercial application of research results, and they suggest that the increasing emphasis on commercial activity may fundamentally change the normative structure of science. (Contains 4 tables, 4 figures and 22 notes.)