Mycoplasma hominis mycoplasmemia was associated with obstruction, manipulation or surgery of the genitourinary tract in 5 adult men. A 4-fold increase in specific antibody titer against M. hominis was demonstrated in serial convalescent serum obtained from 1 patient. Two patients became afebrile after treatment with tetracycline; a 3rd recovered without therapy for a Mycoplasma infection. The 2 remaining patients died of their underlying diseases.