The gene organization and amino acid sequences of human substance P and neuromedin K receptors (SPR and NKR, respectively) are reported on the basis of molecular cloning and sequence determination of genomic DNA containing the respective receptor gene. The human SPR and NKR genes, unlike many other genes for G-protein-coupled receptors, (G protein, guanyl-nucleotide-binding-regulatory protein), contain introns which interrupt the protein-coding regions into 5 exons. The human SPR and NKR genes extend over 60 kb and 45 kb, respectively and are considerably larger than the human substance K receptor (SKR) gene consisting of 12 kb. All 4 introns, however, are located at equivalent positions of the three tachykinin receptor genes, suggesting that they evolved from a common ancestral gene. Human SPR and NKR consist of 407 and 465 amino acid residues, respectively, each possessing structural features characteristic of the members of G-protein-coupled receptors. The human and rat receptors show a common tendency of distinctly segmented sequence conservation and divergence among the three receptors, and the observed sequence conservation and divergence would contribute to the emergence of similar but distinct properties of the three receptors. Furthermore, the amino acid sequences and the gene sizes are more closely related between SPR and NKR than between SKR and NKR, suggesting that the SPR gene evolved from the primordial NKR gene after a gene duplication to form the NKR and SKR genes.