The aim of the present study was to evaluate blood contamination of the amniotic fluid collected in 20 patients undergoing a second amniocentesis performed 2 weeks after a first procedure that had failed due to Pseudomonas aeruginosa contamination of the cell cultures. Red blood cell and haemoglobin concentrations in the amniotic fluid were significantly higher in patients who had undergone a transplacental procedure compared with patients in whom the placenta was not traversed with the needle. For both groups, blood contamination of the amniotic fluid was significantly higher compared with a control group of 20 patients undergoing amniocentesis for the first time. Significant blood contamination of the amniotic fluid after amniocentesis occurs in every instance if evaluated at a "second-look' procedure; the blood contamination is higher when an anterior placenta is traversed with the needle. The clinical significance of these findings needs to be further evaluated.