The neutrophilic granulocyte series in the human liver obtained from 109 embryos between 28 to 49 days after ovulation and 76 fetuses between 8 to 22 weeks of gestation was investigated by light and electron microscopy. Hemopoietic cells, considered progenitors of the granulocyte series, and undifferentiated cells first appeared in the intercellular spaces of mesenchymal cells around the ductus venosus of an embryo of 14 mm crown rump length (estimated age: 40 days after ovulation). The early hepatic myeloid progenitor cells which appeared by 50 days of gestation (early stage of hepatic granulopoiesis) differed in ultrastructure from the late hepatic myeloid progenitor cells which first occurred after 50 days of gestation (late stage of hepatic granulopoiesis). These findings indicate that, morphologically, two kinds of hemopoietic stem cells exist in the human embryonic and fetal liver, and that the hepatic granulocyte series in the early stage differs in its process of maturation from that in the late stage. Endogenous peroxidase activity was demonstrated in small granules of the late hepatic myeloid progenitor cells which appeared lymphoid in ultrastructure.