The use of barrier isolators as an alternative to a cleanroom for the preparation of sterile products at ASHP-defined risk levels 2 and 3 and cytotoxic and hazardous drugs is described. The two isolators selected provide enclosed microenvironments. The isolator used for preparing products of risk level 2 has white acrylic and polycarbonate rigid walls that isolate the sterile product from the operator. The isolator used for preparing level 3 products and cytotoxic and hazardous drugs has epoxy-painted steel walls, a front window, and a pair of glove ports; its design theoretically prevents cross contamination between the operator and the product under preparation and between the product and the external environment. An independent contractor familiar with barrier isolators certifies the equipment every six months. A random microbiological sampling is periodically compared with a control. The isolators have been in operation since July 1998 without microbial growth in any sample tested. The barrier isolators cost more than traditional laminar-airflow hoods, but the hospital considers the barrier isolators to be more cost-effective than a cleanroom. A cost saving in supplies for cytotoxic and hazardous drug preparation as a result of a reduction in overall gown and glove use was observed. Barrier isolators offer an alternative to a cleanroom for the preparation of products at risk levels 2 and 3 and offer an aseptic, safe environment for preparing cytotoxic and hazardous agents.