It is well-known that “cook-book exercises” in science and engineering education do not fully realize the learning objectives ascribed to them. Students do learn basic lab skills, but highly instructed exercises do not (by themselves) support theoretical understanding or appreciation of scientific methods. With web technologies we can now design exercises for remote or virtual labs, but we should not expect to improve student learning simply by recreating old didactic problems in new media. Unfortunately studies of the efficiency of different lab types (hands-on, virtual, and remote labs) suffer from a lack of conceptual analysis of what actually constitutes virtual labs. A clarification of these conceptual issues is suggested as part of a Danish research and development project on virtual lab exercises in biochemistry, molecular biology and biotechnology education. The main outcome of this clarification is that specific didactic problems of biochemistry education can now be addressed through the design of exercises in the virtual lab environment.