Recruitment of terminal arterioles and capillaries was studied in the tenuissimus muscle of 16 young urethane anesthetized rabbits. In one set of experiments (8 animals) intravital fluorescence microscopy was used to visualize transverse arterioles and to assess the number of their first order side branches (functionally the terminal arterioles) perfused with red blood cells before and after vasodilation (10(-4)M adenosine, applied topically). In another set of experiments (8 animals) the number of muscle capillaries perfused with red blood cells from the same parent arteriole was determined at rest and during vasodilation (reactive hyperemia), using bright field microscopy. All capillaries and first order side branches that were perfused during vasodilation were also perfused at rest. These findings indicate that in this skeletal muscle preparation no recruitment of arterioles or capillaries occurs in an anatomical sense of the word.