We have cloned the guinea pig neuropeptide Y (NPY) Y1 receptor and found it to be 92-93% identical to other cloned mammalian Y1 receptors. Porcine NPY and peptide YY (PYY) displayed affinities of 43 pM and 48 pM, respectively. NPY2-36 and NPY3-36 had 6- and 46-fold lower affinity, respectively, than intact NPY. Functional coupling was measured by using a microphysiometer. Human NPY and PYY were equipotent in causing extracellular acidification with EC50 values of 0.59 nM and 0.69 nM, respectively, whereas NPY2-36 and NPY3-36 were about 15-fold and 500-fold less potent, respectively, than NPY. The present study shows that the cloned guinea pig Y1 receptor is very similar to its orthologues in other mammals, both with respect to sequence and pharmacology. Thus, results from previous studies on guinea pig NPY receptors might imply the existence of an additional Y1-like receptor sensitive to B1BP3226.