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The decontamination of a range of "in-use" stainless steel surgical instruments by conventional hospital reprocessing techniques was studied, using scanning electron microscopic (SEM) and energy dispersive X-ray spectroscopic (EDX) analyses, with results obtained when an Ar: O2 RF gas-plasma treatment step was added to the cleaning cycle. In some cases, protein contaminants were still retained on instruments subjected to conventional cleaning and sterilization after seven cleaning cycles. No retention of contamination was evident on the surfaces of instruments that were subjected to gas-plasma cleaning. The efficacy of the plasma decontamination is significantly improved by hydration of the tissue residues immediately before exposure to the plasma. The reasons for this are not known, but it is suggested that the production of excited OH radicals and H atoms within the tissue matrix may play some part. Deposition of fluorescently labeled protein from physiological saline solution shows that protein is incorporated into salt crystals formed on stainless steel surfaces. This protein is resistant to plasma etching, but it is shown that water treatment results in improved cleaning. A combination of effects including physical "cracking" of the salt crystals under vacuum and dissolution of the inorganic matrix, which could possibly be accelerated by dipolar heating of the aqueous phase, may be responsible. [ABSTRACT FROM AUTHOR]