OBJECTIVE: Edema clearly has deleterious effects on the microcirculation and, consequently, cell viability. Prior work from this laboratory demonstrated that hyperosmolar microdialysis can reduce tissue edema, but this method is technically challenging. A new, simpler technique of microdialysis using capillary ultrafiltration probes (CUPs) has been studied to determine if CUP microdialysis is as effective in reducing tissue edema in the same animal model. METHODS: Twenty-four Sprague-Dawley rats were studied using a modified McFarlane skin flap. Microdialysis was accomplished using a catheter constructed of four 4-cm hollow fibers that were connected to polyethylene tubing. Catheters on the experimental side of the flap were attached to a vacuum manifold for 8 hours. The control side was treated in 2 ways. In group 1, catheters were placed but not applied to suction. In group 2, no catheters are placed on the control side. Tissue water content was determined by a biopsy-drying technique. RESULTS: Tissue water content was significantly reduced (by paired t test) in both groups by a mean of 3.2 mL/100 g of wet tissue. CONCLUSION: CUP microdialysis reduced tissue water content as effectively as did hyperosmolar microdialysis, but in a simpler and therefore more cost-effective method. The technique could be easily adapted for clinical application.