Data security is becoming increasingly important as the Grid matures. The advances of the Grid have allowed scientists and researchers to share and exchange researchrelated data and information. In reality, however, these specialists do not benefit enough on the Grid. The reason is that the current Grid does not have sufficiently robust and flexible data security. We have been developing a medical data sharing application which allows medical doctors and scientists to share clinical and medical research data securely. This application achieves dynamic transformation of providing data according to the data requester?s attributes using PERMIS. We describe a practice and experience of implementation of access control mechanism build into a medical application using PERMIS.