In a total of 301 placental biopsies in the second and third trimesters, 225 were performed because of suspicious ultrasonographic findings. In this group there was a high rate of aneuploidies (20%). As opposed to the alternative methods for rapid karyotyping, placental biopsies can easily be performed even in pregnancies with abnormal amounts of amniotic fluid. Oligohydramnios and polyhydramnios were key ultrasonographic findings in 38% of cases and were found to be associated with 22% of abnormal chromosomal findings. Suggestive ultrasonographic findings seem to justify the exclusive use of direct preparation.