The medical utilization of sterile solutions for topical, oral, and i.v. therapy and as fluids for patient equipment is increasing dramatically. Currently, approximately half of the nation's hospitalized population receive one or more i.v.’s In the past two decades, attention has focused on the contamination of such solutions by microorganisms and their cellular by‐products. Such contamination has resulted in increased patient mortality and morbidity. Gram‐negative bacteria such asKlebsiella, Pseudomonas, Serratia, Flavobacterium,and several fungi are the principal agents associated with contamination of sterile fluids. These organisms have the ability not only to survive in sterile fluids but also to grow to densities of 105cells per milliliter without visible turbidity. Growth may be accomplished over a brief 24‐hr interval, often in a medium relatively free of nutrients as with sterile water and saline. The water reservoirs and humidifiers of patient equipment which is frequently utilized in intensive care and hemodialysis units have served as sources of contamination and infection. In addition, an alternation in the routine procedure of sealing i.v. solutions by one manufacturer resulted in catastrophic events for subsequent users. Organisms which occupy such environmental niches have been found to react differently to physical and chemical stress than laboratory strains growing on artificial media. The prolonged medical management of debilitated and physiologically compromised patients coupled with continuing utilization of essential equipment, associated fluids, i.v.’s and other solutions increases the challenge to apply appropriate environmental controls to assure patient safety.