Economists and legal scholars have debated the reasons people adopt open source software, and accordingly whether and to what extent the open source model can scale, replacing proprietary rights as a primary means of production. In this study, we use the release by a biotechnology company of similar software under both proprietary and open source licenses to investigate who uses open source software and why. We find that academic users are somewhat more likely to adopt open source software than private firms. We find only modest differences in the willingness of open source users to modify or improve existing programs. And we find that users of open source software often make business decisions that seem indifferent to the norms of open source distribution. Our findings cast some doubt on the penetration of the open source ethos beyond traditional software markets.