7 Oct
                
                    2007
                
            
            
                7 Oct
                
                '07
                
            
            
            
        
    
                4:30 p.m.
            
        grep -v 'HD21 ASN' good.pdb | sed 's/HD22 ASN/HD21 ASN/' > better.pdb Do you have multiple conformations? Then it would be slightly more tricky (but still easy). Ralf