The effects of research ethics training on medical students' attitudes about clinical research are examined. A preliminary randomized controlled trial evaluated 2 didactic approaches to ethics training compared to a no-intervention control. The participant-oriented intervention emphasized subjective experiences of research participants. The criteria-oriented intervention emphasized specific ethical criteria for analyzing protocols. Compared to controls, those in the participant-oriented intervention group exhibited greater attunement to research participants' attitudes related to altruism, trust, quality of relationships with researchers, desire for information, hopes about participation and possible therapeutic misconception, importance of consent forms, and deciding quickly about participation. The participant-oriented group also agreed more strongly that seriously ill people are capable of making their own research participation decisions. The criteria-oriented intervention did not affect learners' attitudes about clinical research, ethical duties of investigators, or research participants' decision making. An empathy-focused approach affected medical students' attunement to research volunteer perspectives, preferences, and attributes, but an analytically oriented approach had no influence. These findings underscore the need to further examine the differential effects of empathy-versus analytic-focused approaches to the teaching of ethics.