Monoclonal antibodies (mAbs) against human natriuretic peptide receptor-A (NPR-A) or NPR-B were produced using NPR-expressing Chinese hamster ovary (CHO) cells and soluble chimeric NPRs consisting of the extracellular domain of each receptor fused to Fc region of human IgG. Three anti-NPR-A mAbs, designated as A144, A397 and A416, bound to human NPR-A but not to NPR-B, while an anti-NPR-B mAb B136 reacted with human NPR-B but not with NPR-A. Competition analysis with the anti-NPR-A mAbs revealed that two mAbs, A144 and A416, recognize an identical or the adjacent site of the receptor and that A397 is directed against another epitope. No anti-NPR-A mAb affected binding of atrial natriuretic peptide (ANP) to NPR-A, while the anti-NPR-B mAb B136 inhibited binding of C-type natriuretic peptide (CNP) to NPR-B. Inhibition of the ligand-binding by B136 is specific in that the mAb showed no effect on the binding of ANP to NPR-A. B136 also blocked CNP-mediated intracellular cGMP accumulation in NPR-B-expressing cells. These results suggest that the region recognized by B136 may be related to the ligand-binding region of NPR-B. NPR-A- and NPR-B-expressing cells were selectively detected by immunostaining using the mAbs. These findings demonstrate that the mAbs will be useful to elucidate the role of the natriuretic peptides and their receptors in normal and disease states in humans [correction of human].