Sidney Farber, world-renowned paediatric pathologist, made major contributions to his field but is acknowledged as the father of the modern era of chemotherapy. He recognised that folic acid stimulated leukaemic cell growth and enhanced disease progression. He hypothesised that folic acid antagonists would inhibit or arrest the proliferation of cancer cells. His landmark study, published in 1948, demonstrated that a number of folic acid antagonists, including 4-aminopteroyl-glutamic acid (aminopterin) produced temporary remissions in children with acute undifferentiated leukaemia. These observations lead to the development and use of other chemotherapeutic agents, either singly or, more effectively, in combination for treating childhood and adult malignancies. He introduced actinomycin D for the treatment of metastatic and localised Wilms tumour. Under his guidance and leadership, both the 'Jimmy Fund', one of the first comprehensive paediatric oncology treatment centres, and the Children's Cancer Research Foundation, which later became the Dana-Farber Cancer Institute, were founded.