The ploidy of placental tissue from 59 abortions was determined using DNA flow cytometry. The specimens were also screened histologically for features considered to be characteristic of a partial mole. Triploidy was found in six cases; three of these cases presented histologically as partial moles. From the four specimens histologically classified as partial moles, three appeared to be triploid. The most specific histologic features of triploidy were cystic change of the placental villi and trophoblastic hyperplasia with vacuolation of the syncytiotrophoblast; however, these changes were also found in some of the nontriploid abortions. Irregularity of villous contours was less specific.