The objective of the present study was to determine the effect of early pregnancy on the sensitivity to, and endogenous production of calcitonin gene-related peptide (CGRP). Contractile responses of arteries of 10-day pregnant and nonpregnant rats were studied in myographs. During contractions induced by 40 mmol/l K<sup>+</sup>, exogenous CGRP elicited an approximately 30% stronger relaxation in mesenteric arteries in pregnancy, an effect not seen in renal and uterine arteries. Capsaicin treatment during K<sup>+</sup>-induced contractions caused a persistent potentiation of the contractile response in mesenteric arteries, indicating that K<sup>+</sup> stimulates the endogenous release of CGRP. This potentiation was similar in the pregnant and nonpregnant state (+81 ± 23% and +82 ± 23%, respectively), suggesting no effect of pregnancy on the endogenous CGRP release. The latter was paralleled by comparable CGRP content in the arteries of both groups, indicating similar tissue CGRP availability. The results of this study support the concept that early pregnancy is associated with a rise in the vascular sensitivity to CGRP in selected areas of the vascular bed without concomitant increase in the vascular CGRP production and release.