Using in vitro and in silico approaches, we demonstrate that the Hmob3 brain-specific sequence is a part of the extended human MAP1B gene 3'UTR encoded by the portion of the exon 7. Previously we had isolated the 1.4 kb Hmob3 clone (Acc. No Y09836) from the human medulla oblongata cDNA library. In the present paper, we report the RT-PCR detection of extended transcripts containing the Hmob3 sequence as well as a fragment of MAP1B mRNA in the human brain mRNA samples. The existence of such transcripts confirms that Hmob3 is transcribed from the MAP1B gene. Thus we report a previously unknown region of the human MAP1B gene which encodes the MAP1B mRNA 3'UTR. The length of the 3'UTR was estimated of 4330 nucleotides. Comparative sequence analysis shows high phylogenetic conservation of MAP1B 3'UTR in mammals. Using Hmob3 as a probe in the Northern blot analysis, we have revealed two different types of transcripts for brain and kidney mRNA samples; in the skeletal muscle sample we detected both transcripts.