We have demonstrated that the entire murine N-myc gene and the sequences necessary for its expression in human neuroblastoma cells are contained within a 7.4-kilobase murine genomic clone. The complete nucleotide sequence of this gene reveals a number of striking similarities and differences when compared to the related c-myc gene including the following: (i) each gene contains three exons of which the first encodes a long 5'-untranslated leader sequence; (ii) the coding regions of the N- and c-myc genes share regions of substantial nucleic acid homology, the putative N-myc protein shares substantial homology with the c-myc protein; (iii) as with c-myc, extensive nucleotide sequence homology exists between the untranslated regions of the human and murine N-myc gene transcripts; however, the N-myc and c-myc untranslated regions are totally divergent; (iv) the N-myc transcriptional promoter differs from that of c-myc and is more related to the promoter of the simian virus 40. We discuss these findings in the context of previously defined similarities and differences in the potential functional and regulatory aspects of these two myc-family members.