The study of endotoxins has undergone cycles of enthusiastic research followed by neglect and revival again due to newly described biological effects attributed to endotoxins. It is almost a generally applicable rule that both extremes in such fluctuations in the popularity of certain re- search fields are unjustified. It is obvious that exaggerated expectations will lead to disappointments, and complete neglect of a once-exciting field is to be followed by renewed attention, if the scientific basis of earlier interest was solid and remained so throughout. The healing ef- fect of fever was praised as nature’s blessed cure, until it was discov- ered that it is caused by bacteria. When it became evident that by careful application one can arrive at therapeutic doses without intro- ducing shock and hypotension, the era of fever therapy began. During this time, indiscriminate use of pyrogens was so widespread that the high expectations had to be followed by disillusionment. Since then, in- terest in endotoxins experienced a few more oscillations, with varying wavelengths and amplitudes, the latest being triggered by the mitotic effect of endotoxin. This led to justified excitement among researchers who study the activation of the cells of the lymphatic system and the consequences thereof, including the release of important mediator mol- ecules. Fever therapy is passe, but the healing that often followed the ap- plication of endotoxins remains a well-documented fact.