Ethical guidelines for research on animals such as the 3Rs (Replacing, Reducing, Refining) and positive harm-benefit evaluations are anchored in EU Directive 2010/63. In this qualitative study we investigated how ethical guidelines interact and/or compete with other considerations when animal research is planned. Four focus groups consisting mainly of researchers involved in animal use were conducted in four Northern European countries and findings were analysed thematically with the support of NVIVO. Practical issues and the importance of doing good science were dominant topics. Practical issues could not easily be separated from the goal of good science. Participants expressed concerns which accord with the core-values of the 3Rs, but in one group they explicitly referred to the 3Rs as a concept. Conflicts between reductions in animal numbers and the risk of creating unreliable results were addressed. They also criticized the practice of using more animals to improve statistical figures to get results published in highly ranked journals – a finding we believe is new. The main conclusion of this study is that ethical values could not easily be separated from the goal of producing good science. Whereas policy makers seem to expect researchers to explicitly take ethical considerations into account, we found that their ethical thinking is mainly manifested as an implicit part of methodology and design. We don’t see this as a problem as long as the underlying core values are implicitly respected, or promoted, in the relevant experimental practice.