The value of DNA ploidy analysis utilizing paraffin-embedded materials in the detection of nondiploid gestations was examined in a year series of 217 spontaneous abortions in first trimester at a hospital. These placentas were histologically classified as follows: 19 hydropic placentas, six partial moles, three complete moles, and 189 nonhydropic placentas. Abnormal DNA content was found in 26 cases (12%). Twelve placentas (5.6%) were triploid, seven were tetraploid, and seven were nontriploid/tetraploid aneuploid. Of the triploid placentas, six were partial moles, one was a hydropic placenta, and the remaining five were nonhydropic. Since large mononuclear cells in villous mesenchyme were observed in the triploid and tetraploid as well as in the diploid hydropic placentas, in which category trisomic gestation was probable, these cells were not considered to be characteristic of trisomic placentas. Although placentas with hydropic villi had a significantly higher frequency of the nondiploid DNA content than nonhydropic placentas, with the exception of partial moles, no correlation between the histology of villi and DNA ploidy was observed. Flow cytometric analysis using paraffin-embedded materials appears to be of value for the retrospective study of spontaneous abortions, especially for assessing aneuploidy.