We have analyzed a 3.8 kb Eco RI fragment of genomic DNA obtained from the amplified N-myc gene of human neuroblastoma cell line BE(2)-C. This fragment contains an exon with an open reading frame encoding approximately 170 amino acids of the carboxy-terminal end of the putative N-myc protein. Comparison of the inferred amino acid sequence of this peptide with that of the 3' domain of the human c-myc protein shows that locally conserved but dispersed regions of homology exist throughout the lengths of these peptides, while hydropathy plots indicate that the physical properties implied by their primary sequences are strikingly similar. Based upon these and other considerations, it is suggested that the 3' domains of c-myc and N-myc may potentially share related functions.