SummaryFive cases ofMycobacterium marinumskin infection in patients breeding exotic fish are reported. Lesions mimicking sporotrÏchoid nodules developed on the fingers, hands or forearms. Cutaneous biopsies revealed chronic inflammatory granulomas consisting of polymorphonuclear cells, lymphocytes, histiocytes, and epitheloÏid cells. Ziehl-Neelsen stain of the tissue sections was negative, but the bacteriological diagnosis was established on Löwenstein-Jensen media. After a few weeks incubation at 30°C,M. marinumphotochromogenic colonies developed. These strains were sensitive to ethambutol, cycloserine, tetracycline, partly sensitive to rifampicin and highly resistant to streptomycin, P.A.S., and isoniazide. Successful treatment was achieved with tetracycline or with antituberculous drugs (rifampicin, ethambutol, P.A.S.) followed or not by the administration of tetracycline. Diagnosis, treatment and epidemiology of the disease are reviewed.