To the Editor.— During the past four years, I have treated six cases (Table) of Mycobacterium (balnei) marinum granuloma of the skin with tetracycline for 8 to 16 weeks with complete healing in all six cases. Positive cultures were obtained in each case and a few acid-fast bacilli were found in tissue in two cases. That involution was spontaneous in any of the cases cannot be ruled out. However, in five cases, the lesions were present for 6 to 36 months and were progressing until institution of tetracycline therapy. The initial dosage was 1.0 gm daily in all cases. Various forms of therapy have been used for M marinum skin infection, including antituberculosis drugs (isoniazid, aminosalicylic acid, ethambutol, and streptomycin), electrosurgery, cryosurgery, and surgical excision. In some cases, none of these modalities may be applicable or suitable due to drug intolerance, location or size of the lesion, or cost.