Several species of bacterial cells were found to adsorb to crystal particles of heavy metals, such as cadmium, zinc, copper, and iron. In particular, Thiobacillus sp. strain 13-1, isolated from a corroded concrete sewer, was rapidly adsorbed to crystal particles of cadmium. Observation under a light microscope revealed that cells of Thiobacillus sp. strain 13-1 were adsorbed aggregately on the surface of crystal particles of cadmium. The bacterial cells that adsorbed were released into the aqueous phase by the addition of carboxylic acid containing negatively charged hydroxyl groups or compounds. Since hydroxycarboxylic acid seems to prevent the tenacious adsorption of the bacterial cells on the crystal particles of heavy metals, the adsorption of bacterial cells to such particles may be attributed to the electrostatic interaction between them.