Three chronic granulomatous Mycobacterium marinum infections of the hand, the result of direct inoculation in a watery environment, are described and the pertinent literature is reviewed. Biopsy revealed caseating and non-caseating granulomas or an intense inflammatory reaction with Langhan's and foreign-body giant cells, and epithelioid cells. Acid-fast stains, when positive, showed bacilli somewhat larger and longer than Mycobacterium tuberculosis. The diagnosis was established by culture on Lowenstein-Jensen medium at 30 degrees centigrade. Treatment included débridement and synovectomy combined with antituberculous therapy. On the basis of available in vitro and clinical evidence it was concluded that the preferred antimicrobial therapy is a combination of rifampin and ethambutol and that surgical excision is often necessary.