Biochemical perculiarities of the potato tumours development on the plants infected with the agent of cancer Synchytrium endobioticum (Schilb). Perc. The experiment is dedicated to ascertaining contrast biochemical peculiarities of tumours on potato plants infected with the agent of cancer. The results of researches were used for the detection of the disease agent, its differentiation and identification of pathotypes of the cancer agent in the centres.