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Treatment of schistosomiasis is now simple and control protects millions in Brazil, China and Egypt and many thousands in other countries. It is difficult, therefore, to visualise the frustration and despair of scientists and clinicians in Africa, and in Egypt in particular, at the beginning of the century faced with a disease described as 'perhaps the most dreadful of the remaining plagues of Egypt' (Madden, P.C., 1910). It was known to be caused by a trematode worm (discovered by Bilharz in 1852), but apparently with a life-cycle atypical of other parasites of that class in that the worms are unisexual and that no intermediate host had been identified. The cause of the disease was known but there was no treatment, and the question 'How are people infected?' remained unanswered. Rational preventive and control measures would be possible only when this question was answered. Investigations to answer it, and early attempts at control, constitute the basis of the following historical review. The controversies, theories and fertile imaginations of the eminent scientists, that preceded the unravelling of the schistosome life-cycle, are discussed and observations, techniques and ideas of the early researchers that were forgotten only to be rediscovered many years later, are highlighted. (C) 2000 Elsevier Science B.V. All rights reserved.