Neuroglobin is a recently discovered respiratory, porphyrin-containing protein that is expressed in the brain of mouse and human. However, the full-length cDNA sequence and genomic organization of human neuroglobin have not been reported. In this paper, the full-length cDNA sequence of human neuroglobin was cloned following bioinformatic analysis and the rapid amplification of cDNA ends (RACE) technique. It was shown that the full-length cDNA sequence (GenBank Accession No. AF422796) of human neuroglobin is 1909 bp in size, and the genomic sequence is 8041 bp in size (GenBank Accession No. AF422797). To further study the characterization of this gene, the coding region of rat neuroglobin (GenBank Accession No. AF333245) was cloned by using degeneracy PCR. The result showed high conservation among human, rat, and mouse neuroglobin. Furthermore, it was demonstrated that NGB was extensively expressed in rat brain by using in situ hybridization and the immunohistochemical technique. Transcription of NGB mRNA was shown to be widely distributed throughout the adult rat brain, including cerebral cortex, hippocampus, thalamus, hypothalamus, olfactory bulb, and cerebellum. NGB protein immunoreactive cells were also widely distributed throughout normal adult rat brain, including cerebral cortex, hippocampus, thalamus, hypothalamus, pons, and cerebellum. It could be seen that the NGB-immunopositive signals were in the cytoplasma and processes of the neuron. These data strongly support the notion that neuroglobin is a highly conserved gene in evolution and is very important in the nervous system, possibly related to the oxygen supply of the neuron. (C) 2002 Elsevier Science (USA).