Dust particles in hospital pharmacy were reduced to 1/10 to 1/50 by an electric vacuum cleaner placed near the source of dust. The dust removal rate in the area away from the cleaner was lower: 1/3 to 1/15. Dust particles produced in drug dispensing consisted of relatively large ones (1.0-5.0μm in diameter), and most of those due to other factors such as smoking and working personnel were smaller (0.3-0.5μm). Consequently, the ratio of large dust particles of 1.0-5.0μm was higher in pharmacy than in other places, and the ratio of small ones of 0.3-0.5 μm was not so higher. When the vacuum cleaner was placed near the source of dust, most of the large particles over 1.0-5.0μm were removed. Consequently, the particles of this size were reduced in any part of pharmacy. However, smaller particles of 0.3-0.5μm were not efficiently removed in the area distant from the cleaner: particles left unremoved in such area were 3 to 6 folds as many as in the place around the cleaner.