The present paper summarizes our first 12 months' experiences of rapid prenatal diagnosis using commercially available diagnostic fluorescence in situ hybridization (FISH) probes for chromosomes X, Y, 13, 18 and 21. The data clearly demonstrate that the advantage of using FISH as an adjunct technique is the fast and reliable determination of the common fetal chromosomal aneuploidies; the results are available in less than 24 hours instead of the 7-14 days with standard techniques.