Due to the fact that it was the only hospital in Brazil which was exclusively dedicated to these episodes, and, besides, since it was attached to a research and educational institution, Rosenfeld favored from the beginning the systematic observation of patients, resulting over the years in a large and original body of new knowledge about symptoms and treatment of victims of animal poisoning.
Rosenfeld was interested in the study of biochemistry of the action of snake venom toxins in animals and humans, particularly those of the Bothrops family (lancehead or jararaca), which is extremely abundant all over Brazil and which caused a great number of accidents and deaths at his time.
In 1948, as part of a research team at the Biological Institute, Rosenfeld co-discovered, with two other Brazilian physiologists and pharmacologists, Maurício Rocha e Silva and Wilson Teixeira Beraldo, a new endogenous peptide capable of causing a powerful fall of blood pressure on animal preparations, which they called bradykinin.
The substance, a short kinin with nine amino acids only, was detected in the blood plasma of dogs after the addition of venom extracted from the Bothrops jararaca snake, brought by Rosenfeld from the Butantan Institute.
However, the team of Brazilian scientists, including Rocha e Silva, Beraldo, Rosenfeld and Ferreira never came to enjoy the royalties of such discovery, since they always published in the public domain of pure scientific knowledge.