AbstractEffective statistical help to biological and medical research demands thorough involvement of the statistician. The breadth of his activities can be illustrated by considering the questions he needs to discuss with his scientific colleagues in the course of planning a comparative experiment. The paper presents and comments on 22 such questions, showing their relation to the objectives of the experiment, the utilization of resources, and the subsequent statistical analysis. A final paragraph urges that proper attention to all these points forms an integral part of an ethical approach to experimentation.