The organization of the gene of the human myelin basic protein has been established. The gene contains seven exons distributed over 32-34 kb. The nucleotide sequences of the seven exons, extensive parts at the 5' noncoding region and upstream and downstream regions adjacent to the exons were sequenced. A comparison of the nucleotide sequence of the human gene with mouse MBP cDNA and parts of the gene structure of mouse MBP has been carried out. There is a high degree of conservation in the seven exons and the 5'-regulatory and part of the 3'-noncoding region: the nucleotide sequence of the coding region of the human and mouse gene show a 93% homology. As far as the reported 5'-noncoding and upstream regulatory regions of 478 bp are comparable these regions are more than 80% homologous. Primer extension experiments positioned the transcription initiation sites at -55, -82 and -183. In the 5'-regulatory region of MBP gene three direct repeats were found, a nonameric at -401/-416 and two octameric at -192/-216 and -492/-508. A decameric sequence (-256 to -265 from the translation start) is completely homologous to a sequence of the human PLP regulatory 5'-noncoding region.