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."