Although a strikingly modem account of multiple (disseminated) sclerosis was given by Charcot more than one hundred years ago, we are still not sure of the precise nature of the disease, still less of any precise mode of management. Even diagnosis is at best 'probable'. This collection of essays examines the particular difficulties which beset the problem and have mili tated against the solution-problems of data collection and evaluation; clinical and biochemical vagaries and unanswered questions ; laboratory test prediction of the disease, etc. Experts in their fields have set out the difficulties and way forward as ther see them, and there must necessarily be overlap or contradictions which underline our lack of knowledge. Clearly no attempt can be made to cover more than a very few aspects of the problem (a further volume is planned to review other areas not covered here, in particular the relationship between multiple sclerosis and experimental allergic encephalo myelitis)-but it is hoped that the 'softness' of much of the data we have to work upon will become appan!~nt. It is intended that this volume should clearly differ from the large number of monographs and reports of symposia dedicated to multiple sclerosis in bringing out the shortcomings of our approaches, and in some respects our naivities rather than our individual brilliancies.