This is a dosage escalation study to estimate the maximum tolerated dose of drug resistance inhibitor PSC 833 given in combination with paclitaxel. Groups of 3 to 6 patients receive continuous-infusion paclitaxel for 5 days and oral PSC 833 for 6-7 days, following paclitaxel on the first course, then beginning 3 days prior to paclitaxel on subsequent courses.