Drug allergic reactions frequently represent a serious diagnostic problem. In this paper we summarise the most relevant data published in recent years on the diagnostic reliability of the in vitro techniques in drug allergy diagnosis. The lymphocyte transformation test (LTT) offers a sensitivity of 58% in the diagnosis of late allergic reactions to betalactams and 64.5% in the immediate allergic reactions. The basophil activation test and the antigen-specific sulphidoleukotriene determination have an acceptable diagnostic reliability in muscle relaxant drug-induced reactions and in betalactam allergy. BAT sensitivity in betalactam allergy was 50.7% and its specificity 93.3%, whereas CAP had a sensitivity of 36.7% and a specificity of 83.3%, and CAST, a sensitivity of 47.7% and a specificity of 83.3%. For NSAID hypersensitivity, BAT sensitivity was 63.3% and specificity 93.3%, CAST sensitivity was 38.3% and specificity 76.6%. BAT sensitivity in metamizol allergy was 42.3% and the specificity 100% and CAP was negative in all the 17 cases in which it was performed. The joint use of BAT and CAP (specific IgE) allows diagnosis of 65.2% of the betalactam allergic patients with a specificity of 83.3%. The combined use of CAST and BAT in metamizol allergy detects 76% of the cases and 76.9% when associating the skin tests. In NSAID hypersensitivity, the joint use of BAT and CAST does not increase the diagnostic reliability of BAT alone. BAT is a non-invasive useful technique in the in vitro diagnosis of betalactam and metamizol allergy, and NSAID hypersensitivity.