Nm23-H1 gene expression is inversely correlated with tumor metastatic potential in certain tumors, including melanomas, breast carcinomas, and hepatocellular carcinomas. Using nm23-H1 c-DNA primer and genomic polymerase chain reaction (PCR) amplification, we purified three PCR fragments (one of 4kb and two of 2 kb) covering the whole human genomic locus of the gene (8.460bp). We recombined the PCR products into pUC18 and produced a restriction map to perform subcloning. Complete sequencing of genomic PCR fragments, including the whole coding region of nm23-H1, revealed that the gene consists of five exons and four introns spanning 8.5kb. A sequence homology analysis between human nm23-H1 and the homolog gene of the rat (NDP-K beta) shows that exon-intron boundaries are well conserved between these two species.