The effects of exercise and method of administration on the clearance of 57Co-labelled fused aluminosilicate particles from the lungs of male and female animals were studied up to 180 days after exposure. Voluntary exercise (running in a wheel) and the sex of the animals had no effect on clearance. Up to 30 days after exposure the lung clearance rates of particles administered by intratracheal instillation were significantly higher than after their inhalation. At later times the clearance rates were similar. Since intratracheal instillation resulted in long term retention of some radioactivity at the wound site, oral instillation through the mouth and glottis was considered to be a better method of administration.