<p>I need to check programmatically (in .NET) whether a given user (domain account) is a member of the built-in Administrators group on a current computer (the one where the application gets executed).</p>

<p>Is it possible?</p>

You could loop the groups like i did in this answer:
Determining members of local groups via C#
After reading some more, the easiest thing would be to use the
```
System.DirectoryServices.AccountManagement
```
namespace. Here is how it can be used:
http://www.leastprivilege.com/SystemDirectoryServicesAccountManagement.aspx
Sample:
```
```
public static bool IsUserInGroup(string username, string groupname, ContextType type)
{
    PrincipalContext context = new PrincipalContext(type);

    UserPrincipal user = UserPrincipal.FindByIdentity(
        context,
        IdentityType.SamAccountName,
        username);
    GroupPrincipal group = GroupPrincipal.FindByIdentity(
        context, groupname);

    return user.IsMemberOf(group);
}
```
```