The theory about the infectious causes of cancer was very popular at the turn of the nineteenth and twentieth centuries. The research methodology to confirm this hypothesis was based on diagnostic methods used by bacteriology. Various types of experiments were carried out on animals and humans. Attempts were made to "infect" cancer, as well as to transplant cancer cells into healthy animals. Disinfectants were studied looking for opportunities for anti-cancer prophylaxis. They were guided by analogy and empiricism, clinical images of diseases were compared. The aim of the article is to recall research on the infectious theory of cancer with a reminder of the achievements of Polish scientists in this field, and to try to determine the genesis of this theory.