The rationale for conducting this study lies in the premise that if indeed the reason for a limited response of Kaposi's sarcoma lesions and other advanced malignancies to chemotherapy is attributable to a high expression of P-glycoprotein, then, by inhibiting this pump, tumor kill would be enhanced and response rates as well as duration of responses would also increase. Doxil is chosen since recent studies have shown that it is superior to combination chemotherapy with ABV or BV. Doxil is also known to be active in other malignancies such as breast and ovarian cancer (34,35). PSC 833 is chosen since it has been found to reverse P-gp in vitro and in vivo, is non-immunosuppressive, and has been shown in recent Phase 1 studies to be well tolerated.