This study intended to develop a molecular biological method for the determination of the rhesus blood type through the genome of amniocytes. Using micropipettes amniocytes were isolated under a stereomicroscope from amniotic fluid samples. Single or several (> or = 10) amniocytes, respectively, were pipetted into 0.2 ml vials each, and were lysated at 65 degrees C for 15 min using an alkaline solution making the DNA accessible to polymerase chain reaction. Thereafter, the rhesus D gene as well as the CE gene were amplified with nested primers in two subsequent PCR. Finally, the amplification product was electrophoretically analyzed using agarose gel. When single aminocytes were analysed the amplification rate was 64% for the rhesus D gene, and 80% for the rhesus CE gene; "allele specific non amplification" was observed in 24% of cases. With 10 or more amniocytes per vial the amplification rate was 100%. This method permits to reliably predict the fetal rh-type at low costs within about 4 hours.