Exhibit 21

PAETEC Holding Corp. Subsidiaries



|                                                       |  |                                       
|------------------------------------------------------ |  | --------------------------------------
|Subsidiary                                             |  | State of Incorporation or Organization
|PAETEC Corp.                                           |  | Delaware                              
|PaeTec Communications, Inc.                            |  | Delaware                              
|PaeTec Communications of Virginia, Inc.                |  | Virginia                              
|PaeTec Integrated Solutions Group, Inc.                |  | Delaware                              
|PaeTec Software Corp.                                  |  | New York                              
|PaeTec Communications, Inc. Political Action Committee |  | Delaware                              
|PAETEC iTel L.L.C.                                     |  | North Carolina                        
|US LEC Corp.                                           |  | Delaware                              
|US LEC Communications Inc.(1)                          |  | North Carolina                        
|US LEC of Alabama LLC(1)                               |  | North Carolina                        
|US LEC of Florida LLC(1)                               |  | North Carolina                        
|US LEC of North Carolina Inc.(1)                       |  | North Carolina                        
|US LEC of Georgia LLC(1)                               |  | Delaware                              
|US LEC of Tennessee Inc.(1)                            |  | Delaware                              
|US LEC of South Carolina Inc.(1)                       |  | Delaware                              
|US LEC of Maryland LLC(1)                              |  | North Carolina                        
|US LEC of Pennsylvania Inc.(1)                         |  | North Carolina                        
|US LEC of Virginia L.L.C.(1)                           |  | Delaware                              
|US LEC of New York Inc.                                |  | North Carolina                        
|Allworx Corp.                                          |  | Delaware                              
|MPX, Inc.                                              |  | Delaware                              
|Technology Resource Solutions, Inc.(2)                 |  | New York                              
|McLeodUSA Incorporated                                 |  | Delaware                              
|McLeodUSA Holdings, Inc.                               |  | Delaware                              
|McLeodUSA Information Services, Inc.                   |  | Delaware                              
|McLeodUSA Telecommunications Services, Inc.(1)         |  | Iowa                                  
|McLeodUSA Network Services, Inc.                       |  | Iowa                                  
|McLeodUSA Purchasing, L.L.C.                           |  | Iowa                                  



|(1) | Doing business as PAETEC Business Services.
|--- | -------------------------------------------

|(2) | Doing business as Varo Technologies.
|--- | ------------------------------------