Long-term control of mycosis fungoides in the tumour stage was achieved in one patient by daily demethylchlortetracycline therapy. On two occasions widespread nodules and tumours completely involuted within 1 month of initiating this therapy. A second patient showed complete resolution of his plaque stage mycosis fungoides after the institution of oral griseofulvin therapy for a chronic fungus infection. The disease reappeared upon stopping the griseofulvin and involuted upon its resumption. The observations are interpreted as evidence that reduction or eradication of a persistent bacterial or fungal antigen may have a remarkable ameliorative effect in selected mycosis fungoides patients.