A 45 year old male who manipulated tropical fish ponds developed painless nodular plaques in both hands. Biopsy showed mononuclear infiltrate of the dermis with few granulomata. Repeated cultures revealed M. marinum (diagnosis confirmed at the WHO/PAHO Reference Center in Canada). Good initial results were obtained with single agent therapy with ciprofloxacin. The patient suspended therapy after 11 month and a relapse was observed. Definite cure was obtained with oral cotrimoxazole and topic kanamycin.