In this work, we investigate the possibility of biological machining by bacteria as a new technique for metal removal. Some kinds of chemolithotrophic bacteria gain energy from inorganic matter and fix carbon dioxide from the air. One of them, the bacterium Thiobacillus ferrooxidans, "eats" metals. Machining of grooves on pure iron and pure copper by Thiobacillus ferrooxidans is experimentally investigated. The experimental analysis showed that biomachining was possible, since the depth of the grooves generated on the workpiece increased almost linearly with the machining time. Furthermore, electric-field-assisted biomachining proved to be even more effective, because the removed rate became much higher under an electric field.