I have a dropdownlist that loads a list of users from AD. I need to retrieve selected user's properties, e.g. displayName and display it using a label. How do I do that?

The situation is like I have a list of users is dropdownlist e.g. Paul.
I select paul. Click on check button then the code behind generate a search to Active Directory then get the displayName property value and put it in lblDisplayName.Text and refrehes and to display the property value in the label.