The Grid has increasingly gathered the attention and interest of scientists and researchers as a building block technology for computational infrastructure. Because of the recent increasing demands on the Grid, the utilization of the Grid has been explored in various scientific research areas. In reality, however, the Grid is not fully utilized well in today's practical scientific research areas treating security-sensitive data, especially in biomedical research areas. This is partly due to the lack of know-how about how access control can be achieved in the actual applications despite the maturity of security technologies related to authentication and authorization. From this perspective, in this paper, we present a Grid-aware access control mechanism leveraging MyProxy, GSI, PERMIS and XSLT, which we have built into a clinical database for Parkinson's research and diagnosis. In particular, we focus on how these technologies are used to satisfy the access control requirements derived from a clinical database. Also, it is shown that the proposed access control mechanism can be operated with low-cost administration and acceptable overhead.