In recent years, inherited diseases of fetus can be diagnosed prenataly from amniotic fluid and cells obtained by mid-pregnancy amniocentesis. Unfortunately, amniotic fluid provides limited informations to diagnose the inherited diseases and also the fetal condition. However, if fetal blood were available for analysis, more informations then from amniotic fluid could be obtained for diagnosis. For that purpose, 10 samples of blood obtained from amniocentesis incidently were cultured for chromosome analysis. Four of the fetal blood positive cases which were expected as male fetuses by Y-chromatin and X-Chromatin analysis from the amniotic fluid cells showed 46, XX/46, XY in 2 cases, 46, XY in one case and 46, XX in one case. Except 46, XY, all of them were followed up with the results of male infants deliveries. Two of the fetal blood positive cases which were expected as female fetuses by analyzing Y-chromatin and X-chromatin from the amniotic fluid cells showed 46, XX in both cases, One of the both was followed and delivered a female. Four of the fetal blood negative cases were showed 46, XX in all cases and they resulted male deliveries in all as expected by Y-chromatin and X-chromatin analysis from the amniotic fluid cells. In order to obatain the fetal blood, the placental puncture or direct aspiration from the umbilical cord or the chorionic vessel of the fetal surface of the palcenta under the fetoscope can be performed for the diagnosis of the inherited diseases of the fetuses. However instead of intentional placental puncture the blood obtained incidently from the mid-pregnancy amniocentesis or ievitably from the placenta can be used preferably when the fetus was predicted as a male by Y-chromatin and X-chromatin analysis from the amniotic fluid cells. If any complications associated with the placental puncture can be excluded, the placental pucture might be easier procedure for getting the fetal blood.