['Our study was designed to find whether a change in physician ordering of laboratory testing could be obtained by the simple strategy of changing the set-up of the check-box laboratory order form that is embedded in a computerized medical record.', 'This prospective intervention study was undertaken in Maccabi Healthcare Services, a Preferred Provider Organization that has used a computerized medical record since 1992. We examined data from 865 primary healthcare physicians over 3 years. In May 2005 we changed the order form and reduced the number of tests that can be ordered using a check-box form from 51 to 26. Twenty-seven tests were removed from the form and two tests were added. The total number of laboratory test orders and the median rate of test orders per visit to physician during each of the study periods were calculated separately for each test.', 'Tests that were added to the computerized laboratory order form showed an increase of 60.7% in the first year and a further 90% increase in the following year. For the unchanged tests the percentage changes over the same periods were +18.4% and -22.4%. For the deleted tests the change was -27% and -19.2% for the respective years.'] Does format change of a laboratory test order form affect physician behavior?