The effects of sponsorship and financial relationships on the conduct of clinical trials were examined by surveying 321 authors who had published reports of pharmaceutical clinical trials. The survey asked about research sponsorship, financial relationships, who controlled the research, and who carried it out. W hen a commercial s ponsor w as t he e xclusive research sponsor, authors reported less control over and less contribution to the research, and more sponsor control and contribution, as compared with noncommercial or mixed sponsorship. Similarly, financial relationships with firms were associated with less author contribution to and more sponsor control over and contribution to the research. The results raise concerns about bias in the design, conduct, or reporting of research.