Economics is a discipline wlhich adopts a stance somewhat different from most of those represented at this conference. Whilst agreeing that the control of infection is clearly a good thing, economic analysis is based on the tenet that like all good things, infection control is not achieved without cost. Resources will always be scarce relative to the claims made upon them, and the need to make choices about which good things to pursue and which to forego is, therefore, inescapable. Economics also takes a different view of what constitutes a cost. When resources are committed to the control of infection they are no longer available for creating benefits in alternative uses. Thus the true cost of infection control-in economic jargon the ‘opportunity cost’-is seen not so much as the number of pounds and pence involved but rather in terms of the benefits which are foregone by not using the resources in their next best alternative use. There can be an opportunity cost, even if actual financial costs do not rise. For example the time spent by a nurse in taking extra precautions against infection, or the time spent treating infection, is time that could have been spent caring for other patients. That part of economics called economic appraisal (the cost-benefit approach) involves a comparison of benefits gained with benefits foregone, and is undertaken in order tot ensure that scarce resources are employed in that way which creates the greatest benefit from the resources at society’s disposal. This objective is known as economic efficiency (Drummond, 1980). Money is used in the analysis solely to provide a common measure, so that dissimilar elements can be compared. If an infection control programme fails the cost-benefit test, it means that alternative uses for the resources required for the programme can yield benefits elsewhere which are judged to be of greater value than those anticipated from the infection control programme. In a world of infinite resources such choices would not be necessary. Unfortunately such a world does not exist. It is worth emphasizing that at the level that such choices are made, we are dealing with groups of individuals. No one would expect a doctor or nurse to arrange the management of an individual patient’s care solely by an assessment of costs and benefits. The duty of these professionals must be to the patient. However, doctors and nurses can only operate within the limits