In recent years, several research subjects have told us that they had bought or intended to buy stock in the companies sponsoring the clinical trials in which they were enrolled. This situation has led us to ask what, if any, are physician-investigators' scientific, ethical, and legal responsibilities concerning research subjects who choose to buy stock in the companies sponsoring the clinical trials in which they are participating. Although the scope of this problem is unknown and is likely to be small, this commentary examines the scientific, ethical, and legal concerns raised by such activities on the part of research subjects enrolled in early phase clinical trials. In addition, this commentary also outlines the basis for our opinion that research subjects involved in an early phase clinical trial should avoid the financial conflicts of interest created by trading stock in the company sponsoring the clinical trial.