// Get all users from an Active Directory distribution group
public SortedList GetUsersInGroup(string domain, string group)
{
    SortedList groupMemebers = new SortedList();

    string sam = "";
    string fname = "";
    string lname = "";
    string active = "";

    DirectoryEntry de = new DirectoryEntry("LDAP://DC=" + domain + ",DC=com");

    DirectorySearcher ds = new DirectorySearcher(de, "(objectClass=person)");
    ds.Filter = "(memberOf=CN=" + group + ",OU=Distribution Groups,DC=" + domain + ",DC=com)";

    ds.PropertiesToLoad.Add("givenname");
    ds.PropertiesToLoad.Add("samaccountname");
    ds.PropertiesToLoad.Add("sn");
    ds.PropertiesToLoad.Add("useraccountcontrol");

    foreach (SearchResult sr in ds.FindAll())
    {
        try
        {
            sam = sr.Properties["samaccountname"][0].ToString();
            fname = sr.Properties["givenname"][0].ToString();
            lname = sr.Properties["sn"][0].ToString();
            active = sr.Properties["useraccountcontrol"][0].ToString();
        }
        catch (Exception e)
        {
        }

        // don't grab disabled users
        if (active.ToString() != "514")
        {
            groupMemebers.Add(sam.ToString(), (fname.ToString() + " " + lname.ToString()));
        }
    }

    return groupMemebers;
}

This is very useful if you need to populate a dropdown.

Get Members of an Active Directory Distribution Group

directory

C#