Aerosols can be filtered on fibrous filters with or without the pres ence of circulating water. The wet filtration leads to the formation of bubbles within the filter as the carrier gas passes through. This provides alternate mechanisms for the removal of aerosols. Experiments are described to investigate the effects of the irrigating fluid and to compare the efficiency of wet and dry filtration. The results indicate a marked increase in efficiency of filtration of the wet filter as compared with the dry filter.