What are the ethical concerns in Asch?

The main ethical issue to consider in Asch's study is decieving the participants and therefore the lack of informed consent (however, he needed to do this otherwise his results wouldn't have been valid) as well as debriefing. The study may also have caused the participants to experience some distress because when they were debriefed afterwards and found out the aim, they may have felt very embarrassed and mad that they weren't told about it before.