This study evaluated the change of behavior in a group of physicians using direct mailing as a strategy for disseminating information, aimed at the optimization of the use of "Ancillary Diagnostic and Treatment Services" in a regional division of a medical cooperative in southern Brazil. Of the total of 176 physicians, 130 comprised the quasi-experimental study sample. Using the Audit and Feedback method monthly for a year, the ratio between diagnostic and treatment services ordered and consultations provided was fed back to the physicians in the form of graphs. For the analyses, the respondents were stratified in different ways, and the pre and post-intervention and inter and intra-stratum ratios were compared using the Wilcoxon, Mann-Whitney, and Kruskall Wallis tests. Although the orders for ancillary diagnostic and treatment services were fourfold the expected number for the portfolio of policy-holders under the medical cooperative, the group's behavior did not change by providing information without other accompanying administrative measures