This paper shows how concept mapping can be used to measure the quality of e-learning. Six volunteers (all of them 3rd-year medical students) took part in a programme of e-learning designed to teach the principles of magnetic resonance imaging (MRI). Their understanding of MRI was measured before and after the course by the use of concept mapping. The quality of change in individuals' maps was assessed using criteria developed to distinguish between meaningful and rote-learning outcomes. Student maps were also scored for evidence of conceptual richness and understanding. Finally, each map was compared directly with the content of the electronic teaching material. The results show that many of the student misconceptions were put right in the course of their learning but that many of the key concepts introduced in the teaching were ignored (or sometimes learnt by rote) by the students. This was because the teaching material locked these new ideas in structures and terminology that precluded meaning-making among non-experts. Our data suggest that students' prior knowledge is a key determinant of meaningful learning. We suggest that this must be acknowledged if the design and use of electronic teaching material is also to be meaningful. Ultimately, measures of student learning are the only authentic indicators of the quality of teaching through technology.