Despite its widespread use, the antimycotic nystatin rarely causes allergic reactions. We observed a case of acute generalized pustular exanthem with arthralgia and fever, after the oral administration of nystatin. A causal relationship was demonstrated by positive Intracutaneous testing of the drug. Immunohistology revealed positive staining for C3 in the test area, whereas circulating immune complexes could not be identified. These findings are compatible with a type-II allergic reaction. Systemic prednisolone treatment led to a complete remission of the clinical symptoms within 11 days. In two test subjects who had never received nystatin intracutaneous testing was initially negative. After 3 weeks, both developed itching erythematous papules at the injection sites. Therefore, intracutaneous testing of nystatin involves the risk of sensitization.