Abstract The purpose of this study was to test the hypothesis that renal cell carcinoma (RCC) exhibits an increased intratumoral interstitial fluid pressure (IT-IFP). Therefore, resected tumors from human primary (n=23) or metastatic RCC (n=3) were xenografted in SCID mice. The IFP of single tumor nodules (n=65) and normal mouse tissue (n=195) was measured by means of the wick-in-needle technique. Data demonstrate that the mean IT-IFP at neoplasia was 35 times greater than in normal tissue, and decreased precipitously at the tumor boundary. IT-IFP values tended to increase with the grade of malignancy of the tumor cells and tumor size. The mean IT-IFP of xenografts derived from primary RCC was twice as high as that from metastatic RCC tissue. These findings indicate a biophysical barrier to drug delivery in RCC; this may, in concert with cellular-based drug resistance mechanisms, be an additional explanation for resistance of the tumor to certain blood-borne anticancer therapies.