In adverse reactions to drugs with an immunological basis (ADRIB) specific IgE antibodies or sensitised effector T cells take part. Each type of response induces well defined clinical entities. For T cell reactions, classically known as Type IV Gel and Coomb responses, different subtypes have been classified. These correspond to different clinical entitles and each have characteristically histopathological findings. Advanced in vitro studies by development of T cell liens and T cell clones to different drugs compounds and the monitorisation of the immunological response during the course of these diseases has provided new insights for a better understanding and evaluation of ADRIB.