A 45 year-old patient was treated with different drugs for GIT-complaints with diarrhea. Then she developed an elevated skin reaction. We could identify nystatin as causing agent. Under exposition with amphotericin B there was again a systemic reaction with depression of blood pressure and exanthema on the trunk. The patient was never before treated with amphotericin B. The close chemical relationship between these two polyen-antimycotics should be regarded.