This review summarizes the origins of the insight that excess production of pro-inflammatory cytokines caused a constellation of changes that contribute to pathophysiology of disease. This connection was made following the original 1975 TNF (tumor necrosis factor) publication from New York describing how activated macrophages kill tumors. The study caught the eye of a group in London who were trying to understand how the same in vivo macrophage activation would protect mice against the erythrocytic protozoan parasites that cause malaria and babesiosis. Based on collaborative research between these two groups, it was argued in 1981 that TNF and related cytokines initiated events that caused pathology, as well as parasite death within red cells in these infectious diseases. This proved to be a key conceptual advance. It was also argued that the pathology of bacterial sepsis logically had TNF origins. Once TNF was cloned in 1985, allowing its specific analysis in serum and neutralization in vivo, the involvement of this cytokine in infectious disease pathology was pursued by a number of groups. Some researchers found that once "their" cytokine was cloned and sequenced, they had been unwittingly expanding knowledge on TNF for several years. By the late 1980s excess TNF production was proposed to be central to acute systemic viral diseases. This family of cytokines is now at the centre of investigations to understand the mechanisms of acute systemic viral diseases, including influenza and the hemorrhagic viral diseases. With its implication as the master regulator of other inflammatory cytokines in the synovial membrane, TNF has also become the major cytokine in the pathogenesis of chronic inflammatory disease. Its neutralization has proven to be a potent treatment for rheumatoid arthritis and Crohn's disease.