Choices in science--allocation of research funds, selection of research topics, interaction with research subjects (animals, environment, other humans), etc.--often, if not always, include some ethical considerations. Future scientists need skills to deal with and discuss ethical problems, and for that reason we have developed and evaluated one approach to including ethics in a life science curriculum. Our aim has been to support the development of students' ethical sensitivity. The key element in our teaching choices has been the importance of nurturing students' personal moral agency, i.e. their individual skills and responsibilities in moral decision-making, with an interactive teaching approach. The ethics programme was evaluated by extensive course evaluation and using three moral development measures: TESS, DIT and Perry questionnaire. The short ethics programme of three discussions was found to support the development of students' ethical sensitivity. (Contains 2 figures, 1 note and 7 tables.)