A major problem in medicine is the large number of infections associated with implanted and indwelling devices. Silver coating of medical devices is believed to preserve infection resistance. Several in vitro and animal studies as well as clinical observations on silver-nylon, silver-intramedullary pins, silver-oxide-Foley catheters and silver-coated vascular protheses have been interpreted as successful for the prophylaxis of foreign-body infections. Nevertheless, these products have not been established in clinical use. In this study we have been able to present physico-chemical and pharmacological data as well as simple microbiological experiments explaining the reduced anti-microbial activity of silver-ions in some biological fluids.