The vaccines expired a term of validity were incubated with thimerosal (ThM)-resistant bacteria and about 95% of ThM content could be eliminated from the suspension. The conditions were as follows ; vaccines 91, bacterial suspension 0.51, and normal broth 0.51 were incubated at 27°C at air bubbling rate of 0.8-1.21/min. ThM was decomposed to vaporize mercury which was trapped by activated carbon. Safety of the air after passing through the tube packed with activated carbon was tested by using mice ; survival numbers and mercury levels accumulated in the organs were compared to the mice inhaling treated or non-treated air. All mice exposed to the air through the carbon tube were alive (10/10) and showed body weight gain (+0.95g) after 4 d incubation. The mercury levels accumulated in organs of mice were the highest in the kidneys, when the carbon trap was used, but with the carbon trap, only 0.2-0.3 μg mercury per wet g was detected in the kidney and lungs. It is very effective way for the protection of environmental pollution to pass through the carbon tube, although a long exposure experiment of mice has not been done. After treatment by this method, residual mercury was detected at a concentration of 2.46±0.62 μg/ml (±S.D. of 18 runs) in the solution.