The authors examined the potential use of non-radioactive in situ hybridization in prenatal screening. Probes for chromosomes 18, 13/21, 21 and X were applied on fourteen samples of peripheral lymphocytes and nine samples of chorionic villi. The aim of the study was to compare the analyzability of the two different DNA probes for chromosome 21 on six samples of chorionic villi. Six of the nine samples of chorionic villi were hybridized with probes specific for chromosome 21 and all six cases were diagnosed properly. However, we need more data to establish a screening protocol for routine prenatal cytogenetics.