Group Health Cooperative (GHC) of Puget Sound is a prepaid health plan with 285,000 enrollees and 340 physicians. In 1978 a "criterion analysis" approach was instituted to develop medical staff recommendations about preventive care. By 1979, two recommendations evolved discouraging the "routine" use of: (a) chest X rays (CXR) and (b) multichannel blood tests (MCBT) in asymptomatic adults at "routine" physical exams. An extensive educational campaign was conducted to change physician behavior in use of these tests. Usage patterns were measured both before and after the recommendations and educational programs. A fivefold fall in "nonindicated" use of CXR and a 1.5-fold fall in MCBT occurred. A cost savings of $166,582 (annually) resulted from this diminution in "nonindicated" testing. The decision-making process and educational campaign technology hold promise for GHC's preventive medicine program in the future. These results may have applicability to other health care organizations.