The study is about drug patch tests in patients who have history of severe cutaneous drug reaction including Steven Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), Drug-induced eosinophilia and systemic symptoms (DRESS), AGEP (Acute generalized exanthematous pustulosis) and generalized bullous fixed drug eruptions. This study also investigate in Enzyme-linked immunosorbent spot assay (ELIspot) and lymphocyte transformation test. We also trying to prove the correlation among result of drug patch tests, ELIspot and LTT.