The objective of the work was to evaluate the importance of antenatal examination of amniotic fluid and foetal blood in case of suspected Rh isoimmunization of the foetus. In 1991-1992 in 16 patients with a rise of the titre of anti-D antibodies to > 1:8 between the 24th and 36th week of gestation 32 punctures of the umbilicus by means of a 22 gauge needle were made under continual ultrasonic control. In two instances intraumbilical transfusion was indicated. The authors revealed that with the rising titre of anti-D antibodies in maternal blood the foetal haematocrit value in the umbilical blood declines. With the rising bilirubin level the haematocrit declines. In foetuses with a haematocrit of < 31% severe forms of jaundice are encountered more frequently with the necessity of long-term phototherapy and exchange transfusion. The authors did not find a correlation between the haematocrit of foetal blood and the bilirubinoid concentration in amniotic fluid, assessed by Liley's method. Foetuses with a haematocrit higher than 31% are not threatened by severe forms of jaundice and therefore the authors do not use transfusions in these foetuses. Based on hitherto assembled experience, the authors confirmed that cordocentesis is associated with a comparable risk as amniocentesis but provides more accurate information on the state of the foetus.