Study of a patient with recurrent erythema annulare centrifugum of eight years' duration revealed it to be due to hypersensitivity to Penicillium mold of blue cheese. Oral test administration of blue cheese produced a rapid flare and extension of the lesions with a concomitant specific degranulation and decrease in the circulating basophil leukocytes. Complete avoidance of blue cheese has resulted in clinical clearing.