 In 1947 Dr. Rosenfeld started to work at São Paulo's Instituto Biológico, but returned to the Institute in 1951. and in 1954 took over as chief physician at the Hospital Vital Brazil, where he served until 1966.The hospital was founded by Dr. Vital Brazil, one of the world pioneers in the study of animal envenomation and was purposed as a unit of acute care for the victims of venomous animals.As such, Dr. Rosenfeld was concerned about the lack of medical knowledge about the actions of venoms on the human body and its medical therapy, at the time.