Deletion analysis was used to study sites of human Neurokinin A receptor (HNKAR) necessary for signal transduction in CHO cells. Deletion of 62 and 81 amino acids from the c-terminus of HNKAR forms mutant receptors HNKARΔ62 and HNKARΔ81, which bind neurokinin A with high affinity but are functionally different. Wild type HNKAR and HNKARΔ62 are functionally active whereas HNKARΔ81 is functionally inactive. In addition, HNKAR and HNKARΔ62 were both desensitized to the neurokinin A signal within 5 minutes. The data indicates: 1) an intact cytoplasmic tail of the HNKAR is not critical for signal transduction, but the n-terminal amino acids of the cytoplasmic tail are necessary for signaling and 2) the c-terminal 62 amino acids are not necessary for desensitization.