To aid preclinical prediction of immune reactions associated with cytokine release and caused by LMW pharmaceutical drugs and biologics, Alcyomics developed an in vitro human skin explant assay Skimune® involving activation of dendritic cells and T cells. Activated cells are added to a skin biopsy taken from the same healthy volunteer and incubated for 3 days and then routinely fixed and stained with haematoxylin and eosin and graded from Grade I-IV in order of severity. The activated cells are also assessed for T cell proliferation and the supernatants for IFNƴ analysis. Twelve Low Molecular Weight (LMW) drugs associated with T cell-mediated hypersensitivity reactions in the clinic (including abacavir and amoxicillin,)were compared with 5 drugs with rare or no clinical reports including (acetaminophen and cimetidine). Results for T cell proliferation (r=0.6 p<0.01), IFNγ release (r=0.51 p<0.04) and Skimune® (r=0.77, p<0.001) were statistically significant. The Skimune® method was modified for the testing of biologics and 17 biologics were tested. Biologics known to cause adverse reactions such as Campath and OKT3 as well as a TGN1412 analogue gave a Grade II or III histopathological skin response in 70% to 90% of 10 individual tests. There was a positive correlation between adverse clinical outcome and the response in Skimune® (r=0.815, p<0.0001). The present results demonstrate that Skimune® is a highly sensitive assay for predicting drug-induced adverse immune reactions involving acute cytokine release.