Compressed air is known as the fourth utility and enjoys an excellent safety record. It does, however, have a reputation as being to a greater or lesser extent wet, oily and dirty. High technology industries such as the pharmaceutical industry have taken a harder look than most at quality requirements to meet the needs of an industry which can be affected more than most by contamination. In this article, Richard Moore, domnick hunter, UK discusses some of the technology and techniques used in the purification of compressed air for use in the pharmaceuticals industry.