The value of fetal haematological indices in the prediction of intrauterine infection in 91 cases of preterm prelabour amniorrhexis was examined. Cordocentesis and amniocentesis were performed for the diagnosis of intrauterine infection. The patients were subsequently divided into three groups, depending on the results of fetal blood and amniotic fluid cultures. In group 1 there were 53 patients with negative fetal blood and amniotic fluid cultures, group 2 consisted of 22 patients with negative fetal blood, but positive amniotic fluid cultures, and in group 3 there were 16 patients with positive fetal blood cultures. The mean leucocyte and neutrophil counts in all three groups were significantly higher than normal, and in group 3 the values were significantly higher than in group 1. The leucocyte and neutrophil counts were above the 95th centile of the normal range in 58% (22 cases) and 66% (25 cases), respectively, of the 38 cases with positive fetal blood and/or amniotic fluid cultures and in only 15% (8 cases) and 13% (7 cases), respectively, of the 53 patients with no infection. There were no significant differences between the groups, between the patients with amniorrhexis or for normal haemoglobin concentration, platelet count, or lymphocyte count. In the majority of the cases with positive fetal blood and/or amniotic fluid cultures, there is fetal leucocytosis. Since the results of the fetal leucocyte and neutrophil counts are available within a few minutes after cordocentesis, it would be reasonable to give antibiotics to all patients with a fetal leucocyte count above the 95th centile.