[en] Quantitative tissue characterisation by Magnetic Resonance (MR) imaging can be approached by measurement of proton density, relaxation times, blood flow, chemical shift or the use of paramagnetic tracers. This paper is concerned with the measurement of relaxation times and discusses a method which has been investigated both theoretically and experimentally and shown to produce reproducible measurements. The results from in vivo studies of normal and abnormal intervertebral lumbar discs and of patients with dementia are presented. The former confirms the value of the method, whilst the latter illustrates some of the practical problems. (Auth.)