Background: Ethical attitudes and personal values play a significant role in clinical decision-making; however, they have been given limited attention by professionals in laboratory medicine. Studies suggest that individual attitudes are not static and that professionals learn ethical attitudes through a variety of formal and informal learning methods. This study was conducted to investigate changes in the attitudes of clinical laboratory professionals after teaching them ethics and to compare the results among the 3 groups.
   Methods: Four topics were selected in the field of medical laboratory ethics as teaching materials. A questionnaire including 22 items was designed and validated. Teaching sessions for the 3 study groups were held. All 65 clinical laboratory participants completed the questionnaire before and after the classes. Paired t test and ANOVA were used to assess differences among groups.
   Results: Significant differences were found in the mean scores of ethical attitudes before and after the educational intervention among the lecture-based teaching group (p=0.016), problem-based learning group (p=0.001), and all participants (p=0.004). However, no significant difference was found between the mean scores before and after the intervention in role-playing group (p=0.623).
   Conclusion: Teaching by lecturing and problem-based learning was more effective to change ethical attitude of the laboratory professionals than the role-playing method. Thus, we suggest the implementation of teaching ethics using these methods to improve the ethical attitude of clinical laboratory professionals.