Our overall objective is to make a substantial contribution to the cost-containment methodology available to hospitals throughout the country by providing methodology to aid in the definition of laboratory tests of no medical value; by showing that refusing to perform such tests is financially advantageous without being medically deleterious; and by investigating other approaches to laboratory cost containment. To do so, we will implement a computer-based historical laboratory information system, derived from the machine-readable records of the clinical laboratory. The stored information will be used to discover and verify the presence of conditionally useless tests; i.e., tests whose outcome for a given patient can be predicted (well enough for clinical purposes) from information already at hand for that patient. Having discovered and verified the presence of such tests, and having ascertained that the cost-consequences of ordering them are substantial, we will institute a policy of refusing to perform them when the conditions for their being useless are met. We will prospectively study the consequences of so doing by using the information system. To do so we must include in it certain additional diagnostic and other information. These are available in machine-readable form from other hospital systems. Finally, the information system will also be used to investigate other issues related to laboratory cost containment.