Mycoplasma infection was present in the fetuses from three spontaneous abortions and in one second-trimester newborn. Gross examination revealed in most cases a severely infected placenta and membranes, with a fetus of normal appearance. The fetal infection presumably followed placental involvement and appeared to have been acquired shortly prior to delivery. Genital mycoplasmas, Ureaplasma urealyticum or Mycoplasma hominis, were isolated from the placentas and the fetal tissues, and from the genital tracts of the mothers. Isolation of mycoplasmas from the liver indicated that bloodstream dissemination of these organisms occurred in the fetus. In the fetus, the pathologic changes were variable. Lesions were identified in the lung by scanning electron microscopy of the bronchial tree in two cases and were accompanied by interstitial pneumonia. An abnormally dilated left ventricle suggestive of cardiomyopathy was observed in one case.