ATP-sensitive K⁺ channels (K_ATP) couple the intermediary metabolism to cellular excitability and play an important role in the cardio-protective effect of ischemic preconditioning and the activity-dependent autoregulation of cerebral circulation. Although previous studies using PCR and Northern blot suggest that the vascular isoform may consist of Kir6.1 and SUR2B, their expression and precise distribution in various vasculatures remain unknown. To illustrate their vascular expression, we performed this study using in situ hybridization histochemistry. Antisense riboprobes were synthesized by in vitro transcription and labeled with digoxigenin. Distributions of these mRNAs in the various blood vessels were revealed under a bright-field microscope. The expression of Kir6.1 and SUR2B mRNAs was observed in small and intermediate arteries as well as arterioles in several tissues, including basilar, vertebral, mesenteric, coronary and renal arteries. The transcripts were found in arterial smooth muscles. Also, we observed Kir6.1/SUR2B expression in capillary beds. The Kir6.1 and SUR2B expression pattern showed clear overlap, suggesting that they may form heteromeric K_ATP channels in these tissues. The Kir6.1 and SUR2B stains were detected in aorta and renal tubular cells although their expression level was extremely low. In contrast, the Kir6.1 and SUR2B mRNAs were not seen in vena cava, other small veins, myocardium and skeletal muscles. With their strong expression in small arteries and capillaries, it is very likely that the Kir6.1 and SUR2B form the vascular isoform of K_ATP channels in these vasculatures.