Colorectal cancer is a serious medical and economic problem in Poland, as the detection and results of its treatment are very low. Due to this fact, medical research is still conducted in order to find out the symptoms of this tumor and proper preventive measures. According to one hypothesis of carcinogenesis, the process of creating the tumor begins and develops when the balance between the production of reactive oxygen species (ROS) and their deactivation by the "antioxidant protective barrier of the organism" is disturbed. As a result of this theory, it has been decided to examine the plasma concentration of the dietary minerals which work as antioxidants. The results entailed conclusions which prove the free radicals theory of carcinogenesis. They also confirm the part which the antioxidant protective barrier plays in the defence against ROS and their carcinogenic consequences.