On the occasion of a research visit to Thailand in my capacity as a member of the governing board of the South Asia Institute of the University of Heidelberg, I saw for the first time the severe clinical picture of dengue with haemorrhagic symptoms among Thai children. This visit had been made possible by Profes­ sor Dr. med. Dr. rer. nat. Ouay Ketusinh of Bangkok, to whom I wish to express my sincere thanks in this place. In 1972 the German medical literature - the periodical Medizinische Klinik, vol. 87, pp. 152-56, to be precise - had drawn attention to this new phenomenon in the disease panorama of South East Asia, indicating a change in dengue fever from being a relatively benign tropical dis­ ease to a form having serious clinical and epidemiological ramifications. During the ten years following my first publication the new clinical picture, described as "dengue haemorrhagic fever", has become a standard component in the Thailand''s system of notifiable diseases. So too, the World Health Orga­ nization publishes regular reports in its Weekly Records. On March 30/31, 1981, its Regional Office for South East Asia convened a special conference in New Delhi, thus emphasizing the significance of the diffusion of this new clini­ cal picture in the states of South East Asia.