The process of colonization made the colonial administration face terrible diseases in India that threatened the army, white civilians, and the economy of the colony, and generated tremendous insecurities and anxieties. Western medicine and medical men were brought to India to tackle the diseases and protect the ‘crown jewel’ of the British Empire. At the same time, the introduction of Western medicine into India by the British generated a host of complexities that have significance insofar as the history of medicine in colonial India is concerned. What was essential for combating the dreadful diseases was advanced medical knowledge, and it emerged from the sincere and sustained work of medical researchers in India. The scientific efforts of researchers were essential to enabling everything from the diagnosis of the illness to the development of therapeutic treatments. Only by the diligent research of medical scientists—whether it was quinine for malaria, smallpox or plague vaccinations, or anti-kala-azar drugs—was remedial chemotherapy known to the hospitals. The research yielded unquestionably enormous advantages, but to what extent the government appropriately utilized those gains to contain the diseases is another story entirely. It is the painstaking research of the IMS men and members of the Bengal Medical Service that brought to light what we know about kala-azar. Investigations undertaken by them continued until the end of British rule and produced a plethora of information about the disease, its chemotherapy, and its prognosis. This chapter focuses on the growth of medical research on black fever, or kala-azar, against the background of medical research in general in colonial India. It also seeks to shed light on the government's response to it and the extent the research reached fruition.