We describe three cases of extragenital infection by Mycoplasma hominis in three patients transplanted with kidneys from cadaver donors. In two patients, the microorganism was isolated in the exudate from the surgical wound after 72 hrs. of culture on blood-agar (Columbia + 5% horse blood) in CO2 and under anaerobic conditions. In the remaining case, M. hominis was isolated in urine from a suprapubic catheter. All three patients responded satisfactorily to treatment with doxycycline. Mycoplasma hominis should be considered as the possible source of infection in patients at risk because of immunosuppressive therapy and manipulation of the urinary tract. Detection and identification of the organism are difficult without the appropriate techniques.