A re-usable mobile catheterization apparatus was developed that permits multiple blood samples to be obtained from nonrestrained and unanesthetized mice. The collection end of the catheter is located outside the cage allowing the mouse to remain completely undisturbed prior to and during blood collection. The apparatus was used in adult mice surgically fitted under pentobarbital anesthesia with right atrial silastic catheters. Sample volume and collection frequency are easily controlled without subjecting the animal to repetitive trauma. Low plasma corticosterone concentrations confirmed the nonstressful quality of the technique. Full catheter patency in mice averaged 21.5 days. The tethering apparatus design was easily upscaled to accommodate use in adult rats.