In this Phase I study, patients with advanced renal carcinoma will be treated with escalating doses of vinblastine given as a 72 hour infusion, starting at approximately 40% of the total standard dose. A shorter infusion schedule of vinblastine was chosen since there is evidence in other cytotoxic combinations that PSC 833 increases the AUC and decreases the plasma clearance of chemotherapeutic agents by approximately twofold. Cytochrome P 450 3A or CYP3A, which is the major cytochrome enzyme in the metabolism of vinblastine and PSC 833, will be measured during the first and fourth cycle through an in vivo test using a single intravenous dose of midazolam, a short-acting benzodiazepine. Vinblastine and PSC 833 pharmacokinetics will be performed at the same time. For patients with accessible lesions, tumor biopsy will be requested.